On one leg or two legs?

Maril555,
Looks ok to me..... I see the feeder equipment grounding conductor is part of the feeder cable. I assume it connects to the ground bar in the main electrical panel.

Sub panel looks fine. Branch circuits are fed from L1, leg, of the panel.

Branch circuit equipment ground wires are connected to the ground bar.

I see nothing wrong with the installation.

I see you used #10 NM-B, (romex example of), for 4 of the branch circuits. Orange cable sheath signifies #10....
What does the #14 NM-B feed? (white sheathed cable)

Approximately how long are the branch circuit runs?

Maril555,
Are the 4 single pole breaker that feed the #10 wire branch circuits 30 amp?

If so that is a no no... Should be a max of 20 amp.
If the receptacles are 20 amp then the breakers must be 20 amp.

That would not cause your problem though....

The white one #14 NM-B feeds front projector.
Breakers are 30 amp., I don't know, why he used them.
The cable runs are approx. 50-60 ft. ?
I also see one orange 12 awg. cable entering the sub panel- the black (hot ?) wire is not connected to the breaker, terminated with the cap, the white and bare ground are connected to corresponding bars. What's that about, I don't know. Could that cause a problem?
In any case, I'm back to square one. What else can I do???

I also see one orange 12 awg. cable entering the sub panel- the black (hot ?) wire is not connected to the breaker, terminated with the cap, the white and bare ground are connected to corresponding bars. What's that about, I don't know.
01-30-09: Maril555

It appears to be a spare future branch circuit run.

Could that cause a problem?

No
=======

Looking at your picture of the sub panel, the neutral bar on the left side of the panel appears to have a machine screw with a round or pan head on it. The machine screw is near the top part of the bar.
Is that the case?
If that is the case, is the screw head green in color?
Does the screw look like it might be go all the way through the bar and screw, fasten, to the panel enclosure?
==============================

In any case, I'm back to square one. What else can I do???

There is no cable, or TV on the same circuits,
01-29-09: Maril555

But do you have CATV connected to the audio system?

Did you try disconnecting the CATV company's coax cable totally from the audio/video system?

Jea48,
I will have to look at that screw when I get home, but what are you thinking about?
There is no CATV cables connected to my audio system.
The only video cable, is DVI, connecting DVD player to the front projector, and disconnecting it doesn't change anything.
As you probably noticed, the amps and preamp are balanced design, could that be a culprit?
I have a computer in the same room, but it's not connected to audio in any way, and is on a different circuit electrically.