So this weekend I took off the chain, cleaned and lubricated it. I took off the rear wheel. I cleaned the cogs real good to get all the gunk off the freewheel. I then lubricated is using Sheldon Brown's method (although after the fact I realized I didn't have it at a 45 degree angle and it was off the bike, so not really).
Sunday when I went on a ride I noticed a pinging sound coming from the freewheel (or the back of the bike anyway). It almost sounds like a spoke ping, but it happens on every hill. It repeats every couple of pedal rotations as far as I can tell. It might be happening all the time and I just can't hear it at speed.
Tonight I took the chain off and reversed the direction (thinking maybe I had some directional wear after 300 miles). That didn't change anything. I loosened and tightened the quick release thinking maybe it wasn't all the way in the dropouts and I was getting some weird twisting on the chain. I also checked the trailer hitch that's on the quick release. That didn't fix it.
I have an SRAM power link (or whatever it's called). I read that they could be re-used and it went of an off just fine. Don't know if that could be it, if it's just a bit off with it's clearances or something.
So I'm back to the lubricating of the freewheel I think. Could I have added a noise somehow by lubricating it? Or is there something else I'm missing?