The kind of noise you're talking about usually gets in through the amplifier.
There are two pretty common ways that kind of noise gets in.
One is through the amplifiers power supply. If that is the problem you can reduce or eliminate it using a filter on the AC line. I'm calling it a filter because "surge protector" could mean just about anything. But a "real" surge protector (one with at least 12 db per octave responce) is actually a filter. If you have one or want to get one, plug the amplifier into that and see what it does.
Another is inductive coupling. Usually this would happen in the preamplifier section of an amp. Like with the old phonographs (member those) the preamp is very sensitive. If that is the problem you might be able to hear a car's ignition come through the speakers. You might be able to test that by lighting a lighter with a piezo electric ignighter near it.
Another thing you can do is to interconnect the chassis of connected components. If it's a ground issue that will make it stop. But if it does there may be grounding issues in the building you might want to check out.
A new amp might fix it too.
