Gee, and I was going to say it was humming because it doesn't know the words.
All the above ideas could be it. If you have an oscilloscope, you can scope your DC, (or use a digital voltmeter set to AC, and read the AC ripple), to see if you have bad / leaky caps.
The Asteroids boards have caps that dry out. Deluxe isn't that far off - it probably has the same problem.