There's a squeaking noise ("eek-eek-eek") emanating from somewhere under the hood of my '98 S40 whenever I lay off the throttle, and whenever I slowly brake to a halt. And the noise makes a racket in car park speeds (around 20 to 30 km/h). Only when the car speeds up the noise goes away.

What's causing the squeaking? It's been driving me crazy!

UPDATE: During a hour-and a half long drive, the noise gradually went away as I neared my destination.

 

does it do it when the engine is running in neutral and the car is not moving? If it only happens when the car is in motion, then I'd check the brake pads - I've seen them lose all the pad surface and metal on metal makes a terrible squeak...

 

Might be the aux belt tensioner- can you hear it when you open the hood parked?

 

It only happens when the car is moving. thanks!

 

Only popped the hood to check when I did the morning cold start. Did not hear the squeaking. Will look again in different conditions. Thanks!