My sub randomly started making a loud humming noise. The stereo was not even on at the time.

I would check the caps on the power supply. They are rather large electrolytic capacitors that will look like they burst and/or leaking. When these die, the caps ground and the sub will make a loud buzzing sound. If you are handy with a soldering iron you can replace them yourself. Replace them with the same voltage or a little bigger and same with the size.

If the cap. says 16v 4700pF on it, for example, a 20v 5300pF or a 16v 6200mF cap. will work for this application.

check your audio line in connection, either L or R signal line floating may also cause humming noise. Sub woofer usually very sensitive. If your audio input not connected, do you still hear humming noise? in actual you should not hear such noise, unless volume at max then it is possible to hear little.

The symptom sounds like an open signal shield somewhere and the cable is acting like an antenna for airborne electrical noise.

Disconnect the RCA cable at the sub. Is it still humming? NO? Problem is external to it. YES? Internal. Broken ground somewhere.

Recheck all connections making sure to twist the RCA head as you install it so oxides will be worn off.

Consider what may have changed in the environment regarding electrical devices, motors, magnetic sources. Ensure signal and speaker wires as ar not running are as non-parallel to any power cords as practicable.

If I understand this correctly: with NO input or cable attached it hums; with an RCA cable attached it works. (What does 'some' mean in this regard?)

You say that connecting the RCA cable improves its sound. That tells me you're supplying a ground through the RCA cable for stray voltage in the sub.

It seems there may be a basic power issue if it hums with no input. Sometimes a given power source in a home may be wired differently than others or may insufficient grounding, which can result in hum. Try reversing the sub's power plug or move it somewhere else.

Since the sub contains its own electronics it is also susceptible to strong external magnetic fields. Keep it and any signal cables leading to it some distance away from other electrical devices like TV's.

Either you have it configured incorrectly this time around, or the settings are defaulted back to original on your DVR........ adjust your DVR sound properties/settings. and check all wires/connections as well.

Well, I have the same problem and I would think it has something to do with the RCA-connections. If I power up my head unit while I have my main fuse for the amp's removed and then replace the fuse as the head unit is already playing music (thus putting out a current through the RCA-connections) it works just fine. But if I just power up my stereo with the fuse in, my subs go all crazy. I guess it has something to do with disruptions in the rca cable. Maybe they are drawn too close to some power cables or speaker cables? Good luck!

A few more questions-
Does the sub hum without anything plugged into it except for power? If it makes a real loud hum almost a squeal then I think the rca cable between the receiver and the sub is dead shorted and needs to be replaced. If it's more of a low level hum, then it's a ground hum caused by many things, ie........the receiver and the sub being on different power circuits in the house.......sometimes diconnecting the cable tv feed as it enters the room while the sub is connected and humming to see if it stops........the easy fix sometimes is using a 3 to 2 prong ac adapter but lifting the ground on such a powerful amp could be a fire hazard.

I had this issue a few years ago and the power cable from one of the inner terminals had come loose. It was still touching but whenever the sub would really pound it would jump off the connection and then reconnect causing it to hum. It was the most annoying thing ever so I finally pulled off the amp plate (super easy) and you could clearly see the loose wire. I had to use a good soldering iron to put it back on since it's a pretty fat wire. If you're not under warranty anymore then pop the back off and see if that's the issue.

-Dylan

if you have ice buildup then the fridge may be low on freon.
or there is dust clogging around the pump or fan is not running.
remove the bottom or back and look around the compressor.
see that the fan is running.

Hi There, Please advise us what happens when you turn off the sub woofer is the hum still there....??

From YUBEUT.