If you have your devices plugged in on different outlets, you could be getting ground loop noise.
I use a Klein GFCI Outlet Tester model RT210. It costs less than $20 to test for outlets lacking grounds or outlets not wired correctly. I used to take it to gigs to test outlets before plugging in amps and the PA.
Best if you can have all your devices plugged into the same circuit (same outlet). I use a pair of Furman power strips, which reduce EMI and RFI interference and one has regular surge protection and the other one has the rapid detection and shutoff circuit to save my gear from a huge spike.
I would test the outlets first and double check the way all your gear is connected, especially if you have a guitar with a pedal board in the circuit. Some devices have ground loop switches, and when they're all on the same circuit, only one device needs the ground and the rest can turned be off to avoid ground loops. They all will share the single ground.
Other solutions:
- A power conditioner
- DI boxes
DI boxes isolate circuits and that stops noise in its tracks, but that should be a last resort.
If you discover that your house is not properly grounded, maybe from old copper plumbing being replaced with PVC pipes, then you need an electrician to install a ground rod and hook it up to your main breaker.
