Yeah, this makes sense.
The valves were all pretty good, except for one a bit loose. They all were within .203 and .254mm. I tried to make sure they felt the same with the .203mm feeler, just slightly tight. But I have no idea if that is right, really. It's hard to feel the right tightness from YouTube...
It was timed 4k miles ago in the local shop, before I ever drove it. But I suppose the new belt could have jumped.
I can't tell if this is related, but the metallic pinging sound that I heard last summer might be the same as the knock I'm hearing now. I have spent a long time trying to listen to different parts of the engine. It's easy to hear once you notice it, and it seems to be coming from the front of the engine. On close inspection, the only place I can hear it is from the thermostat housing...??? The head just behind that is one of the quietest places on the whole engine, but when you listen to the thermostat housing you get a loud and distinct bell ringing coming and going.
It's frustrating because I have no clue if it really is running well or not. I have very few real life reference points.
I'm at the end of my abilities on this, so I'll have to try to drop it at the shop. Thanks for the help.
By the way, the valve stems look good from the side. But I was unable to get any out to really inspect them. The arms don't come up far enough, even when lose and at full closed position. I'd probably have to release the whole rack of them and pull them completely off the stems to get at the caps.