Bike Forums - a popping noise....

Noises are very difficult to track down using just a forum where no one can hear it live. I would venture to guess the first place to start would be the wheels as you suggested because your there and I think you probably would know to some degree better then I.

So here's what I think may be happening, either your front hub (likely) or your rear hub is not tight enough in the dropout. First loosen the quick release and reposition the front wheel so that it's snug against the dropout, then adjust the quick release by turning both sides of the quick release so that pressure starts to be exerted when the lever is half way from being closed and open, then close the lever. Then do the same for the rear. But I think it's the front. I don't believe a loose hub could make that kind of noise...at least I never heard that before, but you when you remove the wheel grasp both ends of the hub's quick release and try to wiggle back and forth to see if there's any sloppyness in the hub. If there is then the hub will need to be adjusted.

Test the bike and see if this cures it, if not see below.

The other possible problem could be a loose headset. First try clamping the front brake hard, then rock the bike forwards and backwards and see if you notice any play. If so you will need to tighten it enough so that the looseness will cease but the steering is still fluid. If it's still has play you may need a new headset.

If neither of these are the problem lets see how many other replies with different ideas you can get.

If your not sure of what your doing, I'm going to give you a couple of web sites that will show you how including pics, you just have to search the sites till you find what you need.

http://bicycletutor.com/
http://www.parktool.com/repair/