I have been trying to seek out an answer for a good while on this one-

I have strong belt noise on my 90 240DL Wagon. I have been trying to track down the noise for some time.

The noise seems to occur more when the engine is cold and rested but has sometimes popped up after normal running. It will contuine until it feels like something catches- if said "catch" does not take place at slower speeds it ensues even into fourth- if I decelerate the noise dampens and often that is when the "catch" seems to take place. While the noise is present the car seems to not be getting all of its horsepower, it is availble but seems to be delayed- when I punch the pedal it takes a split second to react where as when the noise is not present it reacts flawlessly.

The car has 179K+ on it now- only has two belts now as the AC Compressor went bye bye a few years back and neither belt is showing dramtic wear.

I suspect it could be the fan clutch but I have been told that those almost never go bad- the other thing I have considered is the Alternators Key- I did have it replaced and the noise went away for a few weeks but has now come back and I have not checked to see if the replacement is still in good condition.

Any thoughts?