Strange noise lifting throttle after turbos boosted

[boomerang]

3200GTA, first drives after years.
When driving spirited, occasionally the noise of a mooing cow occurs after lifting throttle.
And no, i am not making a joke
It is as if boost pressure is leaving on a place where it should not.
The engine is a later version with the Kaiser Valve near the brake booster.
Do not know if that has someting to do with this, but something tells me the noise comes from anywhere near the brake booster.

 

[Cyclone1]

From way back in the day, a mooing cow noise was normally associated with a split internal diaphragm of the dump valves. Could be worth checking.

 

[davy83]

could be kaiser valve too

 

[boomerang]

Guess what....my dumb mistake, not tightening the hose clamp around the LH air intake hose enough.
That's wat was causing the noise.
Could slide the hose over the metal tube by hand.

 

[boomerang]

Guess what.....noise still there!
Driving at constant speed, i can trigger the noise by playing throttle slightly.
It is when you just give it just a little throttle, when the mooing comes up.
As soon as more throttle is applied (more boost) mooing is gone.
Also when you lift throttle again, less boost.
Could the small Kaiser valve make such a well audible noise?