strange chirp sound from engine

[crisoton]

hi i have this problem on my w203 c200cdi, ive recently been experinsing this chirping niose from the engine when im driving it kicks in around 2000rpm then goes when i accellerate through , ive changed my belt tensioner pully, idler pully, also new waterpump checked all pulleys for movement n play seem ok, heard about the clutchpully on alternator seems to freewheel fine also took airfilter box off to check rubber mounts they ok cant seem to find the cause, any info would be ace as im at my wits ends cheers chris

 

[Bobby Dazzler]

Is it when you remove your foot from the accelerator? If so then it could be your wastegate leaking boost (by design).

More of a Mewww than a Chirp though. Still a cuddly animal noise that sounds odd.

 

[crisoton]

its like a chirp it comes n goes seems to be a shallow sound then when i press the pedal it gets louder the slowly fades but it doesnt happen all the time its hard to explain its intermittant