Did you buy the car new, and if not, has it done it since you got the car?
e46 window regulators need replacing a lot, and some folks do not put the door back together properly. I ran across several rattling doors when I was car shopping.
I have not had the rear door panels off. but to get off the front, you start by carefully unsnapping the wood trim piece starting at the rear of the door. There is also a screw under the mirror control so you have to snap that up.
If you unplug the air bag, disconnect the battery a while before you unplug the bag, and do NOT reconnect the battery and turn the key on to check window operation while the air bag is unplugged, unless you have the tool to reset the air bag warning light. A Peake airbag tool will read, but will not reset, 2004 and newer.