On one leg or two legs?

I will have to look at that screw when I get home, but what are you thinking about?
01-30-09: Maril555

Looking again closely to the picture it looks like the screw is used to connect the left side neutral bar to the cross tie bus to the right side neutral bar..... I thought at first glance the screw was a bonding screw to bond the neutral to the enclosure. That would have been a no no for a sub panel....
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Just a note.
I think you want to put something on the other side or leg to keep the load some what even. Your breaker from the main panel to the sub pabel my not trip correctly the way you have it. Maybe you should run a 120Vac feed only not 208/230vac to the sub panal.

Hevac1,
It couldn't hurt if Maril555 moved the projector branch circuit over on the other leg, L2, of the sub panel. Might even help in balancing out his main electrical panel.
Will that solve his hum problem? No, jmho.

As for the total load that is connected to L1 leg of the sub panel, I would just about bet the total combined FLA of all the associated audio equipment is 20 amps or less.....

Even when just a power amps connected to the speakers, and nothing else connected to the amps, and with grounds lifted on both amps with a cheater plugs, still I hear faint hum (much louder with no cheater plugs).
I have tried everything:
Unplugged every piece of equipment, and turned off all circuit breakers,
Lifted grounds on every single piece,
01-29-09: Maril555

Maril555,
If your hum problem exists with nothing connected to the inputs of the power amps to the extent you even used ground cheaters on the plugs of the power cords maybe the problem is the power amps and the The Bolero's sensitivity of 92dB/W/m.

(much louder with no cheater plugs).

Again with no ics connected to the amps inputs?
Just the amps connected to the speakers?
Totally isolated from one another?

OK....before you kill yourself and us....pull out your amp and take it to an audio store...or high end used equipment seller....or just a friends house who has some halfway decent speaker (almost anything costing over $100 will do).

Connect the amp with no input to their speaker(s). See if there is a hum and if it changes when you touch the amp case. If it does....fix your home electrical so it's up to code and get your amp fixed.

If there is no hum...come back and we'll work on the problem.