I'm getting an odd 'thumping' noise that seems

[Ray7er 6ers5er3er]

to be coming from underneath the right rear of the car at low speeds. It is like an irregular drum beat. Does anyone have any ideas what this is? And of course it's only periodic

[m6bigdog]

My guess is the rear axle CV-joint.
Once a CV-joint bearing surface gets pitted they will cause a random knocking or intermitten knocking at the rate of the CV-joint rotation which is the wheel speed. Often more noticeable when starting off or accelerating at lower speeds rather than at a constant cruse speed. My Porsche would knock more when accelerating out of a turn in one direction more than the other.

The rear wheel bearings typically cause a higher frequency constant rumble.

The drive shaft center bearing and CV-joint failure indication is similar to the rear axle except the frequency is 3 times the rate of the wheel rotation.

However, if your having other issued like tramlining or rear wheel shake it could be a loose rear wishbones or guide link ball joints.
Rod...
BMWCCA GGC

[bentleyfs]

its the gas tank vent valve to canister is clogged.