HELP! Whistle sound from engine. Boost Leak?

I have a B5 A4 1.8tQM 99.5. When the engine is on, there's a whistle sound coming from the back of the engine. When I step on the clutch the whistle sound goes away. Is this a boost leak or something else? HELP ME! 

If its coming from the back of the engine, there is no turbo or piping going there.  Its most likely a torn pcv hose.

My clutch is weird also, I cracked my oil pan a couple months ago, going over a curb. So I replaced it and ever since, my car vibrates when in first gear, taking off. And at 2-3000 rpm, there's a loud warp sound coming from the engine..

There are several types of whistles...  Hopefully its not the dying turbo "siren".  Do you get any odd colored exhaust when you first start the car?

I have a little bit of the same problem, when i am standing still, i push the gas and get a little whistle for the first split second of throttle. Would it be in the turbo portion even though its before 2k? I don't notice horrible MPGs, I get like 300-350 per tank half city, half highway. I have a new DV, so that is not the problem...I don't mean to thread jack, I just have a similar issue.

Theres no weird color coming out of my exhaust but I've been getting real bad gas millage also besides the whistle sound. I know that it's definitely a leak and something to do with the clutch.

I think this noise is the least of your issues!