Hum noise from speakers stops on activity

Question

Well, this is a pretty interesting problem that I'm curious about, and couldn't think of any reason for it to happen.

This is the case:

My microlab speakers are producing an annoying hum/buzz when computer plays music for quite some time. I can't tell for sure, but I think it started after I had a problem with my computer, which in order to fix it I needed to replace the battery on my motherboard. Since then my computer clock seems to be off (after turning on the computer the clock is right, but after some time it starts to be late, and that happens about 80% of the time, which is weird as well since there are times when the clock is fine). The second problem that happened is that the speakers started buzzing when music is played. (No buzzing/humming when there is no sound played). When connected to another device (for example my smartphone) the speakers work fine.

The weird thing I noticed today (and I don't know how I haven't noticed before), is that when I perform some action on the computer, for example moving my mouse cursor or typing on the keyboard, the humming noise almost stops.

Things to note:

1. Both my keyboard and my mouse are connected via USB.
2. My speakers are connected through an audio jack.

My guesses is that it may be connected to small power surges applied when there is an activity from the keyboard/mouth, or due to more CPU usage made by this activity but I almost have no hardware understanding and therefore can't know for sure, and that's why I ask the question here. I also find this question pretty intriguing.

Thanks!

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Update 18/06:

I have connected a DAC through a USB to my PC, and my speakers to the DAC and the noise stopped (The sound output from the computer is now a digital output converted to analog for my speakers).

Now, the DAC is my friend's, and I want to find a permanent solution for my problem. Does it help in isolating the problem finding a solution (that does not involve the purchase of a DAC/new soundcard) or is the only option left is indeed buying a DAC/soundcard?

Thanks!

Answer 1

Hum in audio is almost always a ground-loop problem. Your computer PSU and your speaker power plug are two paths to ground, so sometimes ensuring that you plug them both into the same plug strip/outlet is enough to resolve the issue.

The reason your smart phone does not hum is probably because there is no ground loop: the path to ground is only through the speaker amp.

One of the other answers also points to over-amplifying a low-volume signal. You wind up with a lot of amplification of the noise as well as the signal, and computers emit a lot of EM noise. It almost sounds like you have the volume at 2 on the computer and 11 at the amp. Try setting (and forgetting) the computer volume to 80% and then adjust the volume on the amp.

Also ensure you are connected via the proper output: if you connect a line-out to high-z (i.e. impedance mismatch), then you wind up with noise and quality problems as well. Most often, you want the "green output."

If you have an optical out (aka SPDIF/digital out) and a corresponding optical (digital) input on the amp, try using this instead.

As far as the clock is concerned: time drift is the norm for electronic clocks. You probably need to set up an NTP server in your time/clock settings.

Answer 2

Guess: When you replaced the battery, you touched your mainboard, and either because you held the battery or because your hands were statically charged, the resulting electrostartic descharge damaged some components on your mainboard slightly. This causes both your clock to run unreliably, and it also causes your internal soundcard codec chip to pick up noise from the surrounding components, either because some coupling doesn't work anymore, or because something else started to produce noise, more than the internal soundcard can filter out.

When there is USB activity, the electrical pattern on the mainboard changes, and this either makes the electrical noise disappear, or it cancels it sufficiently.

Ways to test: Connect your speakers an external USB soundcard, and the hum should disappear. Connect your speakers to an interal soundcard, and the hum should disappear or become less, because while the soundcard is still in the case so it can pick up EM waves, it's now farther away from the part of the mainboard that's broken. Produce some other USB activity (USB flash stick), and see if the hum also disappears.

Answer 3

One reason could be that you have some audio-enhancing software installed which automatically adjusts the volume. I use i.e. Breakaway. This increases the volume if the original volume is low and it decreases the volume if the original volume is high. This software works well i.e. for playing music videos with different volume levels.

But if the volume is very low then this software might increase the volume a lot and this could create this problem. Breakaway has for that reason a noise-reduction filter to make sure this does not happen. But your software, if you have any like that, may not have noise reduction (enabled).

I would try to boot the PC just into the BIOS and look what will happen. If you still have noise then it's clearly a hardware issue. You could also try to boot Windows or Linux from a CD or memory stick and check if you have the same problem.

Answer 4

As dirkt said, it could be caused by an electrostatic discharge when you installed the new battery. As an old hardware repair guy I would first try to get back to the original state before you replaced the battery. It is possible that the battery you installed was bad. One way of checking is to just remove the battery. You will have to set the time manually after booting up but at least you will have eliminated one variable. Also check to see if you have the proper replacement battery especially if it does not have the same number/code as the original.