I’m glad to see that cpd, the original poster, was able to eliminate the hum problem without requiring major rewiriing or drywall work. As it turns out, the solution took more than one single modification. Not surprising.\n\nI’m also put off by TLS Guys tone in his last response. It was offensive. The rest of my comments are directed at him and not the OP.\n\nFirst, let’s reiterate the known details of the OP’s problem. (Pay close attention to the sectons I've bolded.)\n\nThe OP had audible hum through the loudspeakers during phonograph playback. He explained that his phonograph cartridge was connected to an older Marantz stereo receiver’s phono input, using it as a phono pre-amp, and then out from Tape Out jacks to a Denon AVR via RCA interconnects.\n\n\nThose RCA cables, containing line level audio signals, exit the back of the cabinet where they ran behind drywall adjacent to an electric power line for the LED lights. This inaccessible space was between the wall and the back of the cabinet.\n\n\nA photo showed the turntable, three LED lights, and Marantz receiver (containing the phono pre-amp and FM tuner) were close to each other. It did not show where the dimmer light switch was located. Nor did it show the Denon AVR, speaker cables, or speakers.\n\n\nThe hum occurred only during phono playback, and only when the LED lights were on. The OP did not mention what other sound source devices he used, but he did say an FM tuner built into the nearby Marantz receiver did not suffer from any hum with or without the LED lights. Furthermore, this tuner operated without any antenna. I assume the antenna connection jack was left unoccupied. This suggests the OP lives in an area with strong FM signals, strong enough to dominate over many sources of interference. But it also suggests the unoccupied antenna jack could allow RFI to interfere with FM radio playback from a shielded radio receiver.\n\nHow to fix the problem? First try #1, and if it doesn’t eliminate the hum, try #2 and #3.\n\nRelocate the RCA interconnects running between the Marantz stereo receiver and the Denon AVR, such that they don’t run nearby the power line for the LED lights.\nReplace the dimmer switch for the LED lights.\nReplace the LED lights themselves.\n\nThe OP first, relocated the wires described in item 1. This may have partially reduced the hum, but did not eliminate it. The OP next replaced the dimmer switch with a standard on\/off wall switch, and that did completely eliminate the hum. His results suggest that RFI generated by the LED dimmer, entered the system by the phono level cable between the turntable and the Marantz pre-amp, by the line level cable between the Marantz pre-amp and the Denon AVR, or both.\n\nTLS Guy's lengthy explanation indicates how RF interference, such as that generated by LED dimmers, could generate an audible hum in the presence of unshielded solid state amplifiers driving loudspeakers. If so, the OP would hear that hum regardless of the sound source. Yet, while using the FM tuner in the Marantz receiver, no hum could be heard while the LED lights were on. TLS Guy's lengthy explanation fails to address that.\n\nBut your efforts at schooling the readers of this thread does succeed at insulting their intelligence. I speak for myself. But I wouldn’t be surprised if others felt as I do.\n\n\nWell I'm sorry if I offended you or anyone else. That was far from my intent. I did mention that turntables and cartridges are a special case.\n\nI did not address the tuner issue and probably should have.\n\nHowever the thing about RF interference is that it is hit and miss and at first glance appears to not make any sense and be totally confounding. That is because if you look at the crystal radio circuit the penetration of RF depends on a degree of random tuning of the affected circuits. In other words whether the an RF signal generated in the home will penetrate a given device or input depends on whether the circumstances are right for a circuit to tune or resonate with the said RF interference. The randomness of all this makes it so hard to predict. This also makes it next to impossible for designers of equipment to make it totally immune from any possible RF hash.\n\nSo the take home for designers of AV equipment and unfortunately home designers is to try and take steps not only to minimize generation of RF hash but more importantly reduce its opportunities for spread, distribution and reception. I see this as a bigger and bigger issue going forward with far better recognition and understanding of the issues involved.\n\nAs you can see from the OPs response unless you have at least some elementary understanding of electromagnetic propagation and reception by inadvertently tuned circuits these issues when they occur, and they will, will be hard to cure. This does require at least some understanding of electronic circuits and especially function of components like inductors, capacitors and solid state junctions. Earth loops are bad enough, but this issue is on a totally different level.\n\nOnce again I'm sorry for any offense, but this is an issue that needs much wider discussion and further understanding as sources of RF hash increase and proliferate.\n\nI think this forum has a stellar record among these sort of forums and being more often correct and able to resolve issues that people bring to us than many others. That is entirely due to the selfless devotion of many members here to which you Swerd, have contributed to immeasurably.\n\nAt the end of the day do not loose sight of the fact we solved the OP's issue.