You need to get your car in for a safety check with your mechanic as soon as possible. "Clunks" can be from any number of sources, but most often the source is wheel bearings, hubs, CV joints, or brakes. All of these, if damaged or worn, can create an unsafe driving situation. If you are a do it yourself'er, then you should safely jack the car up (flat surface, using multiple jackstands and following the owner's manual recommendations) and remove the wheel to inspect/locate the source of the noise. Good luck with it!
〉 Answered on Feb 11th, 2013 by Karen Salvaggio, Owner - Professional Race Car Driver at Thunder Valley Racing