Update on 96 C280 tensioner noise.
I removed the tensioner pulley, I have the spring loaded tensioner with the 92mm diameter pulley, and the bearing apeared to be fine. I did notice that it didn't take much force to loosen the nut that holds the pulley on when I removed it. When I installed it and tightened the nut finger tight I noticed that the pulley had some play on the mounting bolt/stud. It made me think that there should be a bushing on this thing. So, I tightened the nut real tight and now the noise is gone!
About 400 miles ago, I had the head gasket replaced, and the only thing I can think of is that an apprentice mechanic tried to loosen the belt tension by turning the wrench to the left as an inexperienced one might be prone to do and lossened the nut a little bit without realizing it. I also found that several of the radiator hose clamps were not as tight as they should be and clamp on the lower hose where it attaches to the water pump was stripped although it wasn't leaking, yet. I can't imagine how long this has been like this. I changed the uppper radiator hose and thermostat last week - installed a behr - and the old hose looked so good I didn't change the others. Should be pretty good with just 44K miles.
It is not often that one can fix a problem without buying parts.