I have a 1999 Audi a4 quattro. When I bought it I didn't hear any noise from the turbo. Then bought a boost gauge to make sure it was actually working. Hooked it up and says it's getting 5-8 or so psi. And ideas on why I can't hear the turbo?

 

1 because its a pea sized turbo, 2 because its low boost, and 3 because the stock turbo inlet pipe and air box dampens the sound with reasonator.

 

+1 ^, if you want to know its there you can do the following: Get an aftermarket intake, chip the car to increase boost, get an aftermarket DV. Then youll hear an ever so faint whine under boost and a woosh sound on the shifts from the DV.