New to Hoster and forum

[ddouglass]

Your hum problem comes from a lack of good ground for the building. Older buildings did not have 3 prong plugs when built and so didn't have a ground on any of the circuits. They may have added newer 3 prong outlets but may not have added the 3 wire wiring.
In those locations you will need to use the 3 wire to 2 wire converters. You can find these in your hardware store.
On your second problem can you explain this a little more in detail? Are you saying the music in the older bars is lower volume than the newer ones or are you saying the music tends to fade in and out?
If it is that the volume seems lower, then this is probably an acoustic problem and an equalizer may help with that.
If it is that the music is changing volume level as in going up and down, then this is a power problem and you may damage your equipment playing there. The only thing I could think of that would help would be a battery back-up for everything. That would level out the power and keep your equipment from being damaged by the up and down swing of the incoming power.