What is this squealing noise on startup? (video)

[mouse]

My ABY coupe has a 'belt' squeal noise when starting from cold - a video is attached.
Some squealing can also be heard sometimes when increasing revs during the first 30 to 60 seconds of the engine running, but it goes away after that, and does not squeal on startup if the engine has recently been running, only if the engine has been off for a number of hours.

A change of all belts (timing belt, alternator belt, PAS belt, Air Conditioning belt) water pump and relay roller at the last service did not solve issue (the squeal was there before and after the service).

Any ideas on likely causes or troubleshooting steps?

[John.]

Maybe after sitting for a while the battery has discharged a little and is drawing more amps from alternator after starting engine ?...…...so alternator is working harder.

[SwallownAmazon]

Almost certainly alternator belt - did you tighten it after it was changed? Mine was changed last year and needed almost an inch of slack taken up after "bedding in".

[Ebra]

Mouse - any luck fixing this issue? Mine does the same. Thanks

[mouse]

No, still does it. I had the belt tension checked and apparently all ok but still squeals a bit

[Tractor Dave]

I had the same and I thought the belt was tight enough. My VAG mechanic corrected me. The ribbed belt needs to be drum tight to function properly.

[steve briance]

You could easily eilimate / identify the alternator belt causing the squeak by taking it off.

No squeak when conditions say it should and there is your problem