Hi. I wonder if anyone can help. Ive got a 93 WRX and its making a noise when on boost. As strange as it may seem the only way that i can describe it is like a high pitch farting noise. The car boosts fine but when reaching peak power the noise starts. Any ideas? Thanks in advance.

 

The noise has now gone but the car still wont boost up properly. One moment its fine then the next the car just wont pull at all. It just stays at the same revs and speed and wont go any quicker. Someone help?