Get the tires thoroughly inspected for rot and cracks. (You can do this yourself by removing each wheel and inspecting the inside and outside tire walls.) The whining could be your power steering pump (does the noise change when turning the steering wheel?) or maybe the alternator. You may want to change the tranny fluid, as well, if it hasn't been done.

The belt is inexpensive and easy to replace if it hasnt been done in awhile. Can remove the belt by using a 17mm socket and rotate the tensioner counter clockwise, stick something small in the hole to keep it in that position. New tensioner comes with a metal pin in it holding it under tension. While it was off I spun the pulleys and noticed the groove one making noise like a skate board wheel so replaced that also, the smooth pulley seemed fine. Put the old belt in the trunk with the spare tire in case I need it in an emergency. Can check the back of your Operators manual for the belt size. Manual has some other usefull info like spark plugs. Should also tell you the sub-model of your Mercedes, which is helpful when looking up parts diagrams. Mines a 2010 C300 4matic Sport (204.081)



I went with the continental 6K2404 (2404 is the size in MM) belt which fits great. My tensioner was also not running smoothly, it looked like it was bouncing back and forth so replaced that too. The original Mercedes tensioner is just a Gates tensioner, stamped Gates right on the back. And the pulleys are INA brand.







Blue arrow for 17mm socket. Red is the locking pin.

Thanks for all of the info. I think I will change the belt and look at the condition of the tensioner.

The whiney noise is coming from the right side of the engine, so im suspecting alternator like you said above. Going to get my stethoscope to have a closer listen. Do they usually start whining when they are on their last breath?

Who knows? When I have had one go, it just went. But that was on an Audi.