I as well suffer from the "marbles in a can" noise coming from the driver's side firewall/under foot area. It sounds like it's right down by the parking brake/door speaker (which inexplicably blew, and now sounds awful).
Curious if anyone has any updates on this or things to check other than the exhaust clamps. Also, where do you all find 93 octane gas? All the stations around where I live in the Redmond, Wa area only have up to 92 octane.
Cheers!
Evan