It might be a worn TAB or some other rear bushing letting the rear axle move around in the turn. A shot TAB can cause all sorts of bumps and thumps coming out of turns and when you accelerate. Not to mention that slight wandering sensation at higher speeds on a straightway. Besides the TAB there are other bushings back there on that axle that can wear out and let things thump and bump.

Might be worth getting the pumpkin up in the air, getting both jack points on stands, and then getting a bit of light on the subject. Pull the tire off the side where the noise seems to be coming from and see how much play the axle has from front to back. Don't get too carried away with the car on the jack stands, you feel side to side sway and that points to TAB.

Then as already suggested check things like the rear brake shoes and the e-brake pads. They are hidden behind the rotor and get missed since they are out of sight.

Good Luck,

Paul