So a couple months ago I messed something up in my car by overrevving it. I changed the pushrods and had a compression check done, and it all turned out ok. Replaced a plug wire that was burnt and it ran good except for a slight stumble around 3000RPM. Then I took it to the track a couple weeks ago. After my second run, I noticed it was backfiring, not loud, but somewhat constant. So since the compression was good before, and the plugs were brand new, the wires all looked fine, I decided to pull the opti I replaced last summer and check the rotor. Here's some pics.

The rotor looks a little rusted over, does it always look like this?


Also pulled the coil wire and it looked kinda grimey



I guess if both these things check out, what else could be causing my backfire? Could one of the rockers have come loose? I have poly-locks and felt them all, none of them felt loose. Any help would be good for this n00b, thanks guys.