After zero problems for the first 4000 miles, I am experiencing a faint rattling noise that sounds like rocks in a can. This noise occurs most in third and fourth gear on an '07 MC 6 Speed. I suspect it is coming from the exhaust sytem. Anyone dealt with this?

 

Have the dealer take a look at the exhaust heat shielding. If it's making contact with ANYTHING or loose anywhere it'll buzz & rattle as described. Horrid sound, but easily fixable.

 

Thanks, that was what I suspected it to be. Unfortunately I once had Mustang 5.0 with a similar sound. The dealer was never able to fix it -- claimed it was normal. Hopefully, I'll have better luck with MINI service.