Hi all, I was trying to figure out a front-end click in my drivetrain of my fixed-gear MTB when I noticed that the chain tension varies pretty dramatically during the pedal stroke. Something must be bent or out of round?

My plan is to fix that something, repack the BB, and see if the click goes away. The problem is that I don't know exactly what to do next. Possible sources of the problem:

1) the chainring (steel 32t, a bit worn) could be out of round
2) (the crankarm/spider on the Truvative "power spline" cranks could be bent
3) the BB could seated funny or messed up in ways I don't know about
4) ???

Does anyone have advice about how to diagnose and resolve the problem? I prefer to do all my own wrenching and I'm on a budget. My instinct is to buy a new chainring, but they are expensive and I would hate to replace the chainring only to find that the chain tension continued to vary. Replacing BB is even dicier as I don't think the "power spline" BB is still in production, and my cranks only mate with that spindle.

Here is a mostly irrelevant picture of the bike just so you don't leave the thread empty handed.