First - with the radio on and the noise present, disconnect the antenna from the radio. Note whether the noise is still present or not. Then reconnect.
IF the noise is still present with the antenna disconnected, the noise is coming in via the power leads. If the noise stops, it's obviously coming in via the antenna/feedline.
Next - bring a battery into the radio room and connect the radio to it. You're just going to be listening so the battery doesn't have to be a huge one. A motorcycle or lawnmower battery would be fine for this purpose. NOW, with the radio turned on and the noise present, open the house's main circuit breaker. If the noise disappears, turn the main back on and start opening individual breakers, one at a time, to identify the circuit that's making noise. Then, start unplugging everything that's powered by that breaker.
If this old technique doesn't identify the problem (i.e. you have the main breaker open and the noise is still present), then you'll need to check for noisy street lights, neon signs within an amazingly wide radius --
Oh, and you'll need to reset a bunch of clocks, most likely.
