Please help newbie

Ok I just bought my second BMW ever I had an M3 years ago until it was rearended... any how I bought this one as a fixer upper the body has seen better day engine is sound trans is soundish however when accelerating until I get above 20MPH ish it feels like the middle of the undercarriage is getting rattled by the driveshaft.... could this be a Trans mount? Guibo? I'm lost and just had back surgery so I can't really get under her to look around just curious of any one's ideas....
Thanks,
Ryan