I use a LW radio receiver tuned to 198kHZ LW, BBC World service in the UK, I am in France so the signal is weak.
Some days I get the BBC, some days I get the Russian service from Moscow a few thousand miles away, as they seem to both share the same frequency.
Anyway, I use the LW radio receiver to listen to a fairly wide band of bleed from electrical installations. Laptops are the worst and bleed all over the place. Mobile phones when being charged are also bad bleeders. Here in France their electrical transmission lines also kick out a fair bit of interference. Just so beautiful when the main utility Power Grid is out, as their is such peace on the airways.
Kitestrings, I actually use the LW receiver method to check my OzInverters bleeding, and ensure that my shielding steel cabinet is well earthed and doing its stuff.
Modern PSU seem to be the most culprits.
Interference suppression is not my field, but their are specialist's out there that should be able to help.