Ohh no, is it sorta like a chirping noise? Well i had a chirping noise in my engine and it turned out that 87' 300E's had many problems with there blet tensioners and they usally had to be replaced once during the life of the car. Heh, i also thought it was a bearing, so did my dad until our mechanic told us the above info. Once you isolate the problem, call up mercedes if your a DIY and order it (it's a kit). I had mine installed it was a total of $500 but we got ripped off so id say like 350.
Good Luck, your car will run and sound like new once this is fixed.