by yardman » Wed Jan 16, 2013 2:37 pm
From what you describe, it could be a wheel bearing.
Does it happen for one specific wheel? If so, check the tyre wear is even and where possible raise the wheel off the ground, grip the tyre around the tread at opposite sides and try to rock from side-to-side.
Rock the wheel in various places around the tyre - if you can feel play in it then that's most likely the problem.