Strange sounds after going off throttle

[minim]

Short explained is that if I am at third gear and give wide open throttle at 3000rpm and leave the pedal or clutch out at 4000rpm I get this steam train (in lack of words) sound. I also feel that I might not have full power on third gear and up and it might be related to this. This happens if I keep going at third gear also so its not just happening when I increase 1krpm. I tried to get it on video even if it's not easy to hear anything trough a mobile camera and I will post the link below. The car is a RS2 -94

http://www.youtube.com/watch?v=-rd2cQuInGc&feature=youtu.be

I can't get to the car in the next two weeks so I'm just speculating in what could be wrong and will make myself a list of todo/thoughts/tests to do once I get back home.

Suggestions:
-check orientation and operation of N75 - By Thecrispynoodle
-check crank pulley to see if it's close/into the intercooler - By 4WDrifter
-check for heat shields or similar rubbing drivetrain - By Thecrispynoodle
-check rear diff mounts - By Thecrispynoodle

Todo:
- change small vacum hoses in the intake system. Changed the ones that was leaking but want all changed so I don't run into this problem with the ones that isn't changed yet.
- try to get a used ISV that is not leaking. Only a very little leak at it (1bar test) so I don't think this is related to my problems with the sound atleast. Could be causing problems with not giving me 100% power.
-try to find out what's causing the memory error code that vagcom is throwing. I dont' get other fault codes but that what all I had time to check. 65535 - Internal Control Module Memory Error

Tests:
-

Done:
-fixed airleaks in the intake system (except the isv mentioned above)
-new spark plugs
-changed from open filter to OEM filterbox+new filter
-new oem resirc valve



Since I've been googling like mad to figure out what could be wrong with my car I figured that putting it up here might give me some good hints. Can't really do much about it until I'm back from work but if you want to help out getting me in the right direction of what to look at I'll read up and be ready to go

[Thecrispynoodle]

By resirc valve do you mean the turbo bypass valve? Have you checked the PCV valve under the inlet manifold? Have checked correct orientation/operation of N75 valve?

[minim]

By resirc valve do you mean the turbo bypass valve? Have you checked the PCV valve under the inlet manifold? Have checked correct orientation/operation of N75 valve?

I ment the valve that is resirculating air into the inlet hose right aftern the MAF when going off throttle. The aftermarket one that was in there was also mounted in the wrong orientation so it is like Audi made it now.

I did replace one valve down there but I don't think it was the PCV. It was the one way/non return valve that I swapped with a new one.

Noted your suggestion to check orientation/operation of N75. Thank you

[Thecrispynoodle]

PCV is the small cylindrical one that joins to the T hose under yhe inlet manifold it's not easily visible. The large diameter end points up I think check the Quattroworld FAQ. If you hear whooshing somewhere you clearly have a boost or vacuum hose issue somewhere. Does it idle ok as high idling and 561 dtc's is also sign of leaks.

[minim]

PCV is the small cylindrical one that joins to the T hose under yhe inlet manifold it's not easily visible. The large diameter end points up I think check the Quattroworld FAQ. If you hear whooshing somewhere you clearly have a boost or vacuum hose issue somewhere. Does it idle ok as high idling and 561 dtc's is also sign of leaks.

That's the one I didn't replace. Will change that when I get back since I have to open that hose again to search for/install the missing fire guard that should be close to it.

There are no leaks in the intake system except that very little one in the ISV and if there are they have to be at a pressure over 1bar. I can't hear any leak from the ISV when applying 1bar pressure to the intake but I can spot it when spraying it with soapy water and waiting a bit so bubbles can accumulate but it's really small. Not showing instantly when spraying. Since it's so little I really doubt that this is causing the problem I got with the "steam train sound".

Incase there is a leak above 1 bar I would have to make myself another bung that fits the output from the turbo as I don't wan't to apply more pressure on the "pressure less" side of the turbo. Do you really think this much sound can be caused by a leak that's only showing from 1bar and up? Did you hear the sound on the video?

[4WDrifter]

I listened to your video

Check that your crankshaft pulley isn't split and that it is not hitting against the back surface of the intercooler.

I know this is a completely different tack to all that has been said so far but I had the same sort of noise and crankshaft pulley had split and the front part had moved forward to hit the back side of the intercooler (I have an S2) luckily no permanent damage done. I can't believe how lucky I was the get a second hand replacement pulley within an hour of posting on the wanted section. Put the car up on a lift, remove the drip tray and if the pulley looks okay then I'm sorry for wasting your time.

[minim]

I listened to your video

Check that your crankshaft pulley isn't split and that it is not hitting against the back surface of the intercooler.

I know this is a completely different tack to all that has been said so far but I had the same sort of noise and crankshaft pulley had split and the front part had moved forward to hit the back side of the intercooler (I have an S2) luckily no permanent damage done. I can't believe how lucky I was the get a second hand replacement pulley within an hour of posting on the wanted section. Put the car up on a lift, remove the drip tray and if the pulley looks okay then I'm sorry for wasting your time.

What do you mean by split? I did change the cambelt pulley when I changed cambelt on it recently. I have just used the car for 10km after the change do it could be that something is off there. Do you mean the V-belt pulley or the cambelt pulley? If it's the v-belt pulley was it split in the vibration damber? I tightened the pulley to the correct torque and applied threadlock so I would truly be amazed if the bolt managed to get unscrewed.

Don't worry about me wasting time Love working on the car so all ideas and suggestions are welcome!

[Thecrispynoodle]

I only listened to the video last night, was at work during day - I agree that sounds mechanical not airflow related. Drivetrain mount issues will cause all manner of off-throttle weirdness but normally clunks not continuous noises have you checked centre driveshaft for nearby loose heat shield etc? Worn rear diff mounts allow a lot of unwanted movement IME and you hear it most when off throttle at speed.

[Thecrispynoodle]

I only listened to the video last night, was at work during day - I agree that sounds mechanical not airflow related. Drivetrain mount issues will cause all manner of off-throttle weirdness but normally clunks not continuous noises have you checked centre driveshaft for nearby loose heat shield etc? Worn rear diff mounts allow a lot of unwanted movement IME and you hear it most when off throttle at speed.

If something is rubbing centre driveshaft it will be obvious as you will see rings on it where coating is rubbed off

[minim]

If something is rubbing centre driveshaft it will be obvious as you will see rings on it where coating is rubbed off

Ok. Thanks for the tip.

Starting to get a nice list now and I'm already looking forward to get started On the car

[4WDrifter]

Yes it is in the v belt pulley. The larger diameter end had moved forward up against the back of the intercooler.

I will try to post some pictures though I'm not too computer savvy.

[minim]

Yes it is in the v belt pulley. The larger diameter end had moved forward up against the back of the intercooler.

I will try to post some pictures though I'm not too computer savvy.

Great. If you can't get them uploaded you couald also mail them to me if that is easier. Would be great to know what to look for

[minim]

Finally back home but came home finding that my RS2 was in day to day use cause my allroad had a stuck front brake caliper so I didn't get to check more around this problem yet One thing I did get from this was when I was picked up in the RS2 yesterday and not driving it myself I could hear that this sound came at around 90km/h and when I told the driver to clutch out and play with the rev's the sound still was the same. Leads me to thinking that the sound is coming from somewhere in the drivetrain!

Just waiting on parts so I can assemble the allroad again and get the garage ready for the RS2 and I'll look into what this thing can be.

[minim]

Today I removed the two covers above the exhaust that covers the driveshaft going from rear diff -> front. It doesn't show that the driveshaft have touched the cover and I cannot see any wear/marks on the shaft that indicates that this is what making the sound. It's a nightmare working below the car since I'm not able to get it up in proper working height so before I spend more time under it looking in the blind is there any other spots I should look at? I did not see anything on the front pulley when I checked it.

[minim]

A bit embarrassing since I should have seen this before but the tray below the engine was installed with 3 of 15 bolts/nuts and none of them in the front. The tray has then prolly been pushed down by the wind once I got up to speed and made this sound. There is no holes in the front of the bumper for fixing the tray so I will have to make something that fits between the tray and the bumper so it can be fitted properly. Had a testdrive without the tray mounted now and it's silent