2010 Mazda3 - Reverse question
 

LOUD grinding/shaking noises when I reverse. Only after a night of sitting or after rain.
Not just an annoying noise that I can get over a noise that has the whole back end of the car shaking. I replaced the rear brakes/pads and that's when it started. Contacted Firestone and advised them of the issue. Replaced the front brakes/pads after we spoke then took it in. They advised me nothing was wrong. Issue continued so took to a second opinion where I kept my vehicle overnight so they could hear for themselves. They think it may be rear wheel bearing. Will be taking it back to Firestone again.
I don't want the vehicle until it's fixed... Has anyone heard or dealt with this and what was the issue.