Some questions:
(1) Is it really just on one front wheel and not the other?
If so, definitely something wrong.
(2) Did it just start recently, as opposed to having been there from the beginning/
If so, definitely something wrong.
(3) We all get a "thump" when going over speedbumps (or even any kind of significant bump, like expansion joints)..... but, depending on what you mean by "slow speed" -- like if you mean just a few MPH, it shouldn't be happening. Otherwise it might be just how the car is. Also depending on what exactly you mean by "thump" -- maybe you mean something besides the normal one.