Hello,
Few things that I think might be related, last friday, I heard a huge pop from the rear right, the sound would be as if you dented a sheet of metal and it then returned to it's original state it would make that pop noise.
I assume that noise I heard was my rear caliper piston being stuck and all of sudden unsticking (the noise was very loud, it had the same noise as stated above), had ordered a new caliper at the time but hadn't fitted. It had been sticking over the last few weeks every now and then.
Then today I noticed when going over slight bumps that the rear right is making the sound you get when you drop a bag of tools. Nothing in the boot that would make that sound and I could hear it coming from outside with my windows down.
Then I checked the gap between the arch and the tyre for reason, and the rear right is 2 fingers, while the rear left is 3 fingers. (suspension is standard)