I took precautions in my build to eliminate amp...where did I fail?

I'm building a small music room. One thing I wanted to avoid was amp buzz from my lights. So I asked for advice and took the following precautions:



- I put in a dedicated 20 amp circuit just for music equipment. To isolate the issue, the amp is the only thing plugged in.



- The electrical wiring feeding my lights is run at least a couple feet away from (but in parallel to) the wiring that feeds the power outlets for music.



- I used incandescent lights and a Lutron dimmer. (I know i can spend hundreds to thousands in this department, but had heard/read that I'd be OK with a Lutron.)



Symptoms:



- The buzzing is loudest if the switch is doing any dimming. With the lights at full strength, it's quieter, but it's still there (and pretty annoying). The buzzing goes away completely if I turn the lights off.



- I can quiet the buzzing by touching any metal on the guitar (strings, knobs, etc.). But if I take my hand off, it comes back.



If my lights and amp are on a separate circuit, I don't understand why I'm having this trouble. Thoughts on my situation and how to correct it?

I took precautions in my build to eliminate amp...where did I fail?