Loud noise after shutting the engine off

[Jezinoz]

Hi guys - does anybody have any experience with a loud high pitched whirring noise after turning the engine off in a ‘96 VW 2.5L petrol transporter?
Keeps going for quite a while and it’s pretty loud - (intermittent issue though - doesn’t happen every time...)

[Sunny43.5]

Would you describe the noise as like a cow mooing gently ? if so its the same as ours no big deal other than mooing when you switch of from time to time , you can see they do call them a moo valve on Ebay But as yours is a 97 this may not be the problem . OEM Turbo Solenoid N75 Moo Valve VW T5 Transporter 1.9, 2.0 & 2.5 TDI 1K0906627A 4058633260939 | eBay

[Gold Coaster]

Maybe worn bearings on one of the radiator fans? My 2.0L 96 transporter has two radiator fans and sometimes when the weather is warm one of them (think it's only one) will kick in for a minute or two, when the ignition is turned off, if needed.

[LogicprObe]

Either the radiator fans or the auxiliary water pump is my guess.

[jets]

I was thinking water pump myself. Take a look at the fan & watch to see if the noise stops when the blades stop turning. You would need to touch the auxiliary pump to see if it is running, careful it will be hot.

[benny69]

My 128kw 2.5 TDI is doing the same. Pretty sure the actual mooing sound is the vacuum pump. Still in the process of working out why, thinking the N75 valve could be the culprit.

[LogicprObe]

The 'moo valve' only last for about 2 seconds.
(mine's been doing it for ages and although I have a new valve........I still haven't got around to changing it)

The fans or aux water pump can go a couple of minutes.