Loud rattling vibration in rear end

[Versigirl]

Hoping someone can help! I have a 2003 pontiac vibe, it is an automatic. I have this horrible rattling vibration noise that is coming from the back end. Happens almost every time I drive....usually when I slow down from 100 to 80 kilometers on the highway. Seems to let up when i step on the gas. Not the muffler or exhaust....not the brakes....The car has never had any type of damage to my knowledge, and we have looked everywhere to find a source for this noise! Nothing! Hoping someone on here can help. Thanks

[bluneon]

does the pitch of the sound change when slaloming back and forth?

[A Psycho Martyr]

There's a heat shield above the muffler that rattled on mine for a while.

Kind of a squeaking-type rattle