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I installed a dimmer switch in my bedroom and got buzzing from the switch and from the incandescent light/fan on the ceiling that it was controlling. I took that same dimmer switch and installed it in my daughters room and got no buzzing from the switch or the light/fan. I tried installing a different dimmer switch back in my bedroom and it also buzzed, so it seems to be the location and not the switches that are the problem. Why am I getting this buzzing sound in my bedroom? With a regular on/off switch there is no buzzing, just with the dimmers. I removed the light bulb to see if that was an issue and it still buzzed. Thanks.

Dave McDonald
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    Same fan in each room? Is the dimmer approved for motors? (Most are not.) – isherwood Apr 08 '16 at 19:57
  • The light/fan combos in the two rooms are slightly different, but more or less the same. Both are operating incandescent lights. The fans in both rooms are not connected to the switch, they are both running hot. When I wired in the light/fan, I set it up so the switch only controls the light, not the fan. Because I wired them in this way, I figured I would be able to add dimmer switches to the lights at some point (now). – Dave McDonald Apr 08 '16 at 20:22
  • When you said, "different dimmer switch back in my bedroom and it also buzzed," was the light buzzing, was the dimmer buzzing, or both? – Ben Welborn Apr 08 '16 at 21:21
  • Both the light and the dimmer switch buzzed with both dimmers switches that I tried. – Dave McDonald Apr 08 '16 at 21:54
  • You are right, you should be able to add dimmers in that situation since you are not switching the fan, Maybe it's time to reboot into LED bulbs with smart dimmers, the bulbs are quite good now, payback period is quite short, and it'll even lower your A/C bill. – Harper - Reinstate Monica Apr 09 '16 at 03:38
  • This happened to me as well when I bought LED Dimmable bulbs for a fan. I ended up changing them with GE LED Non-Dimmable bulbs and the buzzing went away. – Outdated Computer Tech Apr 09 '16 at 17:11

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First let me just say, that I noticed that you did not ask, How do I stop a dimmer switch from humming?, but rather WHY is it buzzing (especially, here- not there).

Essentially, your dimmer is also creating or acting like a speaker, because it is physically causing air to vibrate, which is detected by your ear... in other words, sound is created by moving air back and forth. A speaker is made by inducing a magnetic field in an object (like a coil or a bulb filament) which exerts a physical force upon the (induced) object causing it to move and by default, move the air. The range of human hearing is 20 to 20,000 Hz and the frequency of the electricity in a residence is 60 Hz.

The reason it is happening in the dimmer is the same reason as the light bulb; some piece of the dimmer or a neighboring conductor is physically vibrating.

Why it is only in the one spot has to do with something called harmonics... and there is a long physics lecture involved. But in short, harmonic distortions happen because like-waves are additive, meaning that electric wave of similar frequecies (and amplitudes) will add together. The light bulb in the bedroom (or perhaps of the fan motor) and the dimmer are acting like tuning forks each causing amplification (or resonance of waves) in each other and the result is induced power which is strong enough to cause physical movements, and thus, audible feedback.

Of course, from the other discussion about how to stop it, the answer was to change the bulb (that's acting like a tuning fork- not mentioned).

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Ben Welborn
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  • Ben, thank you, that was a good explanation of WHY. I read the HOW thread already before I started this thread and none of it had helped. What really got me was why it was buzzing in one room and not the other. I did try removing the light bulb from the socket and still got the buzzing from the fixture and from the switch, so I concluded that the light bulb itself was not the issue. – Dave McDonald Apr 08 '16 at 21:59
  • Then the tuning fork in question is probably/possibly the fan motor... have you tried disconnecting the power from the motor? – Ben Welborn Apr 08 '16 at 22:02
  • Good call, I'll try that and let you know. – Dave McDonald Apr 08 '16 at 22:04
  • Do you think I would have to actually disconnect the wiring from the fan motor, or just have the fan turned off? – Dave McDonald Apr 08 '16 at 22:05
  • I turned off the fan but the buzzing continued. However, I was able to stop the buzzing by switching the light off at the pull chain (attached to the fan/light combo). That is with or without a light bulb in the socket. So, as you would say, the light fixture itself seems to be the other tuning fork. So it just happens to resonate at a similar frequency to the dimmer and the light fixture in my daughters room does not? – Dave McDonald Apr 08 '16 at 22:20
  • Probably. Resonances are pretty sensitive. An ounce of tungsten in the right place on a car or airplane - gone. But electric lights should not be resonating at all. Something may be falling under the thrall of a magnetic field, either because it is loose, or because you have routed your lamp "hot" a different way than your lamp "neutral" (eddy currents forming in the gap). – Harper - Reinstate Monica Apr 09 '16 at 03:41
  • @Harper "or because you have routed your lamp "hot" a different way than your lamp "neutral" (eddy currents forming in the gap)" Could you explain this a bit more? Could it be a problem with my wiring in the fan/light combo? – Dave McDonald Apr 09 '16 at 15:23
  • All wiring emits magnetic fields proportional to current flow. When both wires in a circuit are parallel and tight, the fields cancel each other out. (Since they flow the same current). When there is a gap (effectively current is going around something) the magnetic field is measurable and has a unit: the ampere-turn. With AC power, the ever-changing magnetic fields induct - this is how transformers work. This can vibrate things. – Harper - Reinstate Monica Apr 09 '16 at 17:15
  • @DaveMcDonald Ok... Just to be sure I understand this, the buzzing continued without a bulb, but with the fan-switch on? If yes, perhaps it is the switch that is vibrating... a new fan-light switch is probably $3 at lowes or home depot. – Ben Welborn Apr 09 '16 at 22:49
  • @Ben Welborn There is a pull chain for the fan and one for the light. The buzzing is independent of the fan, whether it is on or off the buzz is there. The buzzing is dependent on the light. I can stop the buzzing either by turning off the light at the pull chain or at the dimmer switch. It doesn't matter if there is a light bulb in the socket or not. Would you suggest replacing the pull chain switch for the light? – Dave McDonald Apr 09 '16 at 23:17
  • @DaveMcDonald Let me get this straight: you took the lightbulb out of the socket and pulled the pull-switch so that power is supplied to the empty socket, and it still buzzes??? If yes, then it is obviously not the bulb; current is somehow passing through the circuit when it shouldn't be. It may have something to do with either the pull-switch or the socket. But if it's not buzzing (makes sense), then my money says it is probably the bulb but it could still be the switch - or less likely - the socket, or something else. I know that you replaced the bulb, but did you try a 130V bulb? – Ben Welborn Apr 11 '16 at 13:09
  • @Ben Welborn Yes, when power is supplied to the empty socket, it still buzzes both in the socket and in the dimmer. The light fixture for this fan is something I added on, it did not come with the fan. Maybe it is in the wiring? Not sure of the voltage of the bulb, but I'll check it out. – Dave McDonald Apr 12 '16 at 01:20
  • @DaveMcDonald 2 things: first, 130V bulbs simply have a thicker filament, making it more difficult to vibrate, that's all. Second, the bulb is not obviously not the problem. Yes, something is very wrong; current is passing through a (short) circuit when it should not be (no bulb should mean no flow). Since it stops buzzing when you pull the pull-switch off, then the short is at, or after, the switch. Look for burnt or nicked wires, double check connections, trace every lead. Are you certain that you did not attach the fan motor to the dimmer? Sorry, but this is a fire hazard and must be fixed. – Ben Welborn Apr 12 '16 at 13:01
  • @Ben Welborn When you say "the short is at or after the pull switch" I think you mean somewhere at or between the pull switch and the SOCKET, and not at or between the pull switch and the DIMMER. Sorry, I don't have the terminology down yet. I looked at all the wiring in the light kit, everything looks ok. I think what I might try is to buy another, maybe 2 other light kits and see if they cause a buzz as well. If they don't then it is a problem with my current light kit and if they also buzz then the problem is elsewhere. – Dave McDonald Apr 16 '16 at 15:03
  • @DaveMcDonald Yes, I meant somewhere at or between the pull switch and the SOCKET. If you hear buzzing when the pull-switch is on, even when the bulb has been removed, then there is current is flowing when it should not be! That would mean that you have a (dangerous) short circuit, or something else (like the fan) is attached to the switch leg. Current should not be flowing without a bulb. There should not be any buzzing without a bulb. If you have buzzing without a bulb then you have a dangerous problem. – Ben Welborn Apr 19 '16 at 11:36