mmckenna
I ♥ Ø
It is not electrical interference, more like a close frequency that is not exact.
Did you try shutting off the circuit breakers as I suggested?
Often these noise issues that cover a wide slice of spectrum are locally generated. Shutting off devices in your home can help determine that. Might be your cable modem/DSL/router, etc. Cheap USB adapters are notorious for wideband noise.