Have you tried a QRM Eliminator? I haven't tried one myself yet, but I hear good things about them. Also, some really simple things can be really noisy. Cheap LED bulbs for example can be super noisy. I had one above my desk that was terrible.
I think that's a phasing device. You attach an auxiliary antenna specially to pick up the noise. The signal from that is phase shifted and mixed into the signal from the main antenna. The phase shift circuitry has knobs to vary the phase and amplitude. You adjust them so that the noise cancels out.
That can be effective but it's really only useful for cancelling out one noise source. I once used a similar device when there was something bad happening on a power pole down the street. It's no use if you have general noise from multiple directions.
A buddy of mine uses one and it is effective. Most of your noise will come from buck converters and other cheap power supplies in the near field. Cell phone chargers, 120ac to 12vdc PSU, computer PSU, and fluorescent lighting ballasts are big culprits. Plasma TVs will generate more noise as they age. Pole-mounted cable repeater PSU go bad and start heating up, generating a shitload of noise. Any arcing on cracked insulators will generate RFI and can be easily located by driving around with a clear AM channel on your car stereo. Report these as they must also be repaired. Cheap solar panel inverters are also noise generators. A process of isolating house circuits helps identify the offending devices if they are in the home. In most cases, it is unlawful for devices to generate spurious emissions. In the case of solar panel inverters, they must fix/replace them if you complain. Another thing to check is cable tv leakage, which is less of a problem today, but can still cause interference. Unterminated cable coax can radiate lots of noise in the 144mhz band, and also on other channels. Great article about RFI hunting and elimination: https://www.arrl.org/files/file/RFI/Thompson%20Noise.pdf
