weis101

Hi can any body help?
Bought an m plate impreza turbo import about 2 months ago, when u come off the throttle it makes a weird pulsing air sound which was quite loud and as it had a dump valve i thought it was that.
I did not like the noise but thought nothing of it because i was going to change it to a bailys any way, i have just changed it to a bailys which now makes the normal noise but the other noise is still there but not quite as loud and sounds like it is coming from the air intake which has a k&n on if any one knows what it is i would apreciate it i am worried it is the turbo making the noise!
one more thing my check engine light comes on and off two garages have now looked at it but say no faults ware found and cannot put it out any ideas?