Hissing noise

[B5 BIKER]

As the new owner of a 2003 2.5v6 tdi, I am finding my way.
i have noticed when I park the car and turn off the ignition I can hear a 'hissing noise' from the engine bay.
the noise seems to be coming from the area under the plenum chamber cover.
i removed this but all I see is the air con filler connections, but it doesn't seem to be them.
it only seems to last for 5-6 seconds approx.
is this normal? Or is something leaking?
is there a release of turbo gasses automatically after shutdown?
any advice appreciated

 

[gtiboy]

Yep i believe its normal pal mine does it .
Its happens when you have had the air con on .

 

[wesmaster]

yep mine does it too, just the low and high pressure sides of system equalling out.

 

[B5 BIKER]

Ok thanks, will turn it off and see if it happens the next time.
cheers