Rear wheel constant bump
Have you recently replaced a tire or tube? If so, then the tire may not be properly seated.

Remove the wheel, hold it in your lap lying flat, and rotate the wheel around looking at the edge of the rim and tire. You are looking for a "low spot" where the tire appears to "disappear" down into the wheel. It will be slight, but it doesn't take much. My old road bike has 27x1 (630x25) tires, and they can be a challenge.

If you find a "low spot", deflate the tube, put a little bit of dishwashing soap and water on the tire at the bead, and inflate the tube. You may hear a pop sound when the tire bead seats properly into the wheel.