Hi everyone, I would greatly appreciate it if someone could help me diagnose some sounds my bike is making:

I get fairly loud clicking noises when I pedal. It's hard to tell what kind of pedaling causes it. But sometimes there's even a few in rapid succession (often when going over a bump) and then it's almost a ratcheting sound. It's not just a matter of a certain pressure on the pedal, but it's more likely if there's more pressure it seems.

It's almost like the chain slips a little; I feel it, not just hear it.

here are a couple videos of the clicking in action:
http://www.youtube.com/watch?v=OI_DULoAtQU
http://www.youtube.com/watch?v=l0McFGl0XRw

Let me know what you think, or if you want any other info. thanks

(I've searched for a while - the BB seems to be blamed in other threads, but I don't see why it would kind of snap like that or do the rapid clicking sometimes)