Chirp on liftoff

[Colesy]

Have noticed this recently. It's usually at around just under 3k rpm, I lift off the throttle and there's a chirping type sound. It sounds more like air than something mechanical. I'd say it was coming from the turbo/wastegate area. I did try to record the noise but couldn't get any clear recordings. Was thinking wastegate but thought I'd get some pointers before randomly changing things.

[hunker7]

Have noticed this recently. It's usually at around just under 3k rpm, I lift off the throttle and there's a chirping type sound. It sounds more like air than something mechanical. I'd say it was coming from the turbo/wastegate area. I did try to record the noise but couldn't get any clear recordings. Was thinking wastegate but thought I'd get some pointers before randomly changing things.

I'd check if DV diaphragm isn't split. Few years back when I was driving my S4 home I had the noise and ended up being DV.

[UrS4boy]

By-pass Valve BPV) info

Probably the By-pass Valve (BPV) aka "diverter valve" or "cut-off valve". Usually the "honk" like a goose when failed (diaphragm tears).

By-pass Valve BPV) info:

http://forums.quattroworld.com/s4s6/msgs/20994.phtml

[Colesy]

Thanks for the tips, the diverter valve is actually the one thing I have changed so far as I had a spare lying around. There's a chance they are both duff but for the noise to be exactly the same seems unlikely. Sorry for not mentioning this before.

[Colesy]

Any other ideas?

[mike74]

P.C.V. system one way/check valve?
a right beeatch to get to, underneath the throttle body

[Colesy]

I thought I'd check the BOV again as lightening can strike twice. So swapped in another spare and this has cured the noise! Thanks for the suggestions. I really must start throwing away obviously broken parts!!

[hunker7]

If you suck on the vac line it it holds vacuum it's ok of not it's broken