front end clunk

Hey everyone i have been dealing with a bad clunk in my front end for the past couple of months. It is at low speeds and seems to sound like its coming from something rotating(clunk..clunk..clunk). when I hit the brakes the sound goes away. does anyone have any ideas as to what this may be.

Check the caliper bolts or the u-joints in the knuckle.

Ive checked the bolts holding the caliper and they are good and snug but how do i check the u joints?