Photoshopeth

I had a body shop install a Magnapack cat-back after I was rear ended in April.

Well a bad storm was coming through and I was a little too quick to get my car into the garage and put the door down and the garage door brackets came down slightly onto the back bumper and scraped it up pretty good, so I had them re-paint it this week.

They said they didn't need to remove exhaust this time, but the day I got it back, I felt a buzzing at low rpm.

After a small peel out I started getting a metallic pinging/belt slip sounding noise but from the rear end, I thought something was wrong with the LSD at first. But I noticed if the exhaust is hot and I push on the back left exhaust tip I can get it to squeak, if slightly cool, it won't squeak at all. I had body shop readjust and tighten and it still happened.

I don't see anything touching, and everything is as tight as can be, any ideas?