If you have a portable (preferably AM) receiver, you could just try a walk about in the neighborhood, and even without a loop you may get lucky and find the source. You may even be able to track it down with a regular battery powered AM BCB receiver, however often RFI can travel 1000's of feet or even miles on power lines, etc. So usually the best approach is to listen to RFI on the highest frequency where you can find it, even at the top of the HF bands, or even something like an AM aircraft receiver at about 120 MHz. I have used a very cheep thrift store SW receiver which covers several bands of HF and these are probably available for less than $50. Usually RFI is easier to pinpoint as you go to the higher frequencies. Naturally a loop will be a great help.
I would do two additional things. Make sure the noise is not from things in the shack. Also I would temporarily bypass the remote switch and just use a coax jumper, and make sure no wall warts are running anything in the shack. I have a 6 way remote antenna switch, where the shield connections had about a one ohm resistance. Picked up 160 meter noise probably from my house, so used a jumper cable, no noise. Repaired faulty switch design, no noise. So once again....no computers, monitors, etc. just your transceiver right to the antenna for testing.
Also in is not uncommon for things like solar lights and even the battery back up on your home alarm system to cause RFI. A GUESS is that the noise is a SMPS within a few hundred feet of your antenna, although I cannot guarantee this. Happy hunting Rick KL7CW