97 sl320, wholelottamiles. Car has done this as long as I've had it but I'm curious what it is.

I hear it more noticeably on startup but also notice it @ idle. It's coming from the rear passenger area of the trunk, near the battery. It's like a humming/buzzing noise combined.

Anyone have any ideas?

American car for the record, also car shifts hard as hell on some gears occasionally, don't know if this has anything to do with it?