I have dedicated AC with seperate ground, and still have what you describe.
Rather than guess, or have the expense of an electrican, why not take a VOM (Volt Ohm Meter) and plug into your wall socket - just leave it on while you're listening. When the sound starts to change for the worse, check what you line voltage is. If it's going above or below 120 volts when it sounds bad, then you have a correlation and can start working on it - Variac (Monster AVS 2000), power regenerator (PS Audio) or whatever.
If you're at the end of a cul-de-sac with a 50 year old house, the neighbors could put a sag in your current playing with their arc welder or something.
My Monster AVS2000 has seen a 4 volt drop on some very cold nights, and a 6 volt on warm nights (I'm in CT).
For the price of a VOM ($10 at Rat Shak if you don't already have one), it's a cheap way to see whether there's a correlation.
Good Luck
Rather than guess, or have the expense of an electrican, why not take a VOM (Volt Ohm Meter) and plug into your wall socket - just leave it on while you're listening. When the sound starts to change for the worse, check what you line voltage is. If it's going above or below 120 volts when it sounds bad, then you have a correlation and can start working on it - Variac (Monster AVS 2000), power regenerator (PS Audio) or whatever.
If you're at the end of a cul-de-sac with a 50 year old house, the neighbors could put a sag in your current playing with their arc welder or something.
My Monster AVS2000 has seen a 4 volt drop on some very cold nights, and a 6 volt on warm nights (I'm in CT).
For the price of a VOM ($10 at Rat Shak if you don't already have one), it's a cheap way to see whether there's a correlation.
Good Luck