[n00b on demand]

So yesterday I was driving with my windows down and i noticed this very odd noise when i have the car light acceleration. Last year around may i had hear this same scraping grinding sorta noise ( for lack of a better description)....i took it into the shop and the mechanic that changed my donut gaskets said there was a loose bolt. I took it home and everything was fine. Yesterday I noticed the same noise....only happens with light acceleration...doesnt happen under load. Tomssvx said i have a big crack before the main cat...so im going to take it into the shop and see if the guy can weld it for me...that will hopefully take care of that problem. But as for this current issue im going to guess and say its the same " loose bolt" issue. But what the hell could be loose to make a noise like that....it isnt too loud but noticeable...ive noticed it coming from the right side of the car in the rear. Same as last year. I should also mention that 3 times in the past week ive bottomed out backing out of my friends uphill driveway...you gotta back out a certain way so you dont bottom out and of course there were so many cars i couldnt back out that way so the rear side of the car scraped 3 times...maybe thats what caused it