Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hi Robert, noises can be tricky to identify and in the first instance I would remove the V belt to see if the noise does go away when running the engine breifly with the belt removed.
The idler or tensioner pulleys are the most common problems so at least you have eliminated these
We also see problems with the alternator, water pump or the AC compressor - with the idler pulleys you can usually feel if these are worn by spinning them by hand, the other drives are usually less obvious but do try spinning each in turn to see if any feel rough when spinning them
If the noise has gone with the belt removed and you cannot identify which one is at fault by hand then the belt will need to be refitted and I would next recommend using an automotive stethoscope to help pinpoint the noise. These are fairly inexpensive and although I prefer a good quality electronic one the standard cheaper versions can be very helpful in tracing noises
Here are a selection of these: Automotive Stethoscopes
Trying to pinpoint the noise without one of these is very difficult - a long screwdriver to the ear pressed against each drive in turn or a long piece of vacuum tube in the ear can also be usefull but a correct stethoscope is really the best tool to use for identifying noises
Best regards, Paul