Help troubleshooting

[cali_surfer]

I posted this on Chevy Talk, but was wondering if you guys could help me out here. I seem to have a problem. Just recently my motor has developed what sounds to be a knocking noise at idle. My friend and I built the motor a few years ago, but I don't drive the truck that much (maybe has 10,000-20,000 miles on it). It was balanced, 10:1 pistons, Edelbrock aluminum 70cc heads, 234/234 cam, and I run 91 oct. gas all the time. This seemed to happen a few months ago after I installed aftermarket air conditioning on my truck, I don't know why. What I didn't like about the install was the bracket that holds the Sanden AC pump touches the tall valve covers I have, although it doesn't sound like that's making the noise at idle. The A/C pump also needs to be dealt with. I haven't touched the distributor other than setting initial timing. Its a cheapo HEI from one of the big autopart chain stores. Will too much advance at idle create a knocking sound? After idle the motor runs nice and smooth, but at idle it sounds like its rattling from the drivers side of the motor. Oil pressure is good, 30-35psi at idle, 40ish in normal driving range. I'm also going to replace the motor mounts, as they are what I suspect to be the originals (don't know why I didn't replace them when i built the motor). I'm just a little nervous hearing it rattling when i'm stopped at a traffic light or stop sign. Any suggestions or welcome