I have this annoying thump thump sound at between 20-35 mph coming from right rear of car. I've had rear brakes and calipers replaced a year ago, and it kept doing it . frozen caliper issue. My guess is it's some kind of internal baffle in the exhaust that is loose as the muffler is pretty bad looking. It kind of sounds like a rhythmic drumming sound more than a sharp knock.

 

How do you wheel bearings look/feel?

 

I haven't noticed any drag on the wheels, but I haven't actually looked at them,worth a try. It's been doing it a long time, it's getting to the point where I can't stand it . It doesn't seem to get faster much with speed either. but I can take a look .

 

maybe a blown shock?

 

This may seem too simple, and doesn't necessarily fit all your symptoms, but I'll offer it up so you can cross it off the list of things you need to check:

How worn is the tire? If a steel belt is worn thru, it will make a thumping sound as it rotates. I've seen this happen on the inside of the tire where it is not real noticable to see without removing your tire from the car.

 

Rotate the tires and see if the thump thump thump follows the right rear tire.

 

Also Tire balance can cause unwated noises like discribed. If you have crazy uneaven ware on the tire, or almost wave like tread alog one side, have it balanced too!