Bicycle Mechanics - I feel something at the top of the drive side pedal stroke.

This isn't a noise, it's more like a notch, a slight bump in the otherwise smooth revolution of the front drive train, just a little something when I'm at the top of my pedal stroke (drive side). I don't feel it on the left side at all. I've made sure my chainring bolts and cranks are tight, and switched pedals to make sure the problem isn't there. If I'm spinning, I don't feel it. If I am pushing, I do. I don't notice it when I'm out of the saddle.

Any ideas?

square splined bottom bracket? If so, maybe worn at that corner, on that side, only apparent when at top of stroke and starting to press down, crank arm slips on spline?

'Tis square splined. I'm leaning toward something to do with the bb. Unfotunately I have no bb tools, which has kept me a little ignorant about them.

I a ride tonight I find I only feel it when I'm going slow--pushing or spinning doesn't matter. After I get up to speed I can't feel it.

Here is the thread i mentioned in my PM.

http://www.bikeforums.net/showthread.php?t=124065

if it a worn crank on a square taper spindle, sounds like time to replace the crank, according to the thread.