is it a belt problem in my 240d?

[ayrtonsenna]

up until recently, my 240d has run beautifully. not a single problem for almost seven months. all good things must come to an end, of course, a bonbardment of problems hits me all at once. for one, a strange rattling noise began emanating from the undercarriage. this turned out to be a crack in the exhaust stemming from the infamous snow bank fiasco. two, my transmission has begun leaking at a rate that i'd say would be about a quart per month. not a big deal. three, a trip to the lakehouse up in the mountains made the car lose power while going at about 65-70 mph. when i pulled over, the car did not shut off, and i was able to continue. is this an instance of high altitude (it's a minimal increase, but more than the car is used to) or is something else going on? keep in mind it only happened up in the mountains, though it hasnt been on the highway in a while. four, i can feel an oddity in the engine noise of the car. it sounds vaguely like the sound of a washing machine, kind of a rotating sound. it is audible only during initial acceleration from idle, though this could be because the noise of the engine drones it out during driving. i can feel this in the accelerator as well. my friend, a mopar expert, believes it is an issue with the drive belt. is there a way to test this? does that diagnosis seem right? and thank you to anyone who managed to read all the way down to here.