Re 2002 C230K manual transmission, about 87K miles: I've noticed a 'hum' the sound is like running finger around Tibetan medicine bowls- and heard only by sensitive ear. At first I thought tires making sound on different road surfaces; lately only on acceleration, but as of today even off accelerator or idling when stopped, though fainter a distinct hum. Problem is cannot tell if coming from under hood/engine or under vehicle itself.

Before the hum I had a throaty exhaust sound on desceleration; but now that does not seem to be problem. Also intermittently on cold start the I guess computer activation noise which comes from center of dash is loud, grinding and long.

okay so yes I am not a mechanic

I have service appointment but would like any thoughts from folk here- primarily to not have a $$ bill as a result of trying out a number of options- and I wonder could a failing belt produce the hum?