Why does my computer make noise when my cell phone rings?

January 4, 2005 11:11 AM

Does anyone have a theory as to why my computer might make little rhythmic noises for a few moments when, (a) my cell phone is at a minimum 12" near it, and (b) my cell phone is receiving an incoming call? It also does it when I receive or send text messages...
posted by Specklet to Technology (20 answers total)

I don't know why this happens, but when I worked as a relay operator we would hear little clicking rhythms in our headsets whenever someone on the floor sent a text message from his or her cell. It's probably the same phenomenon.
posted by Faint of Butt at 11:16 AM on January 4, 2005

That would be Maxwell's Theory
posted by skwm at 11:17 AM on January 4, 2005

Response by poster: Yeah, I'm familiar with Maxwell's Theory, but what in the housing is making the noise?
posted by Specklet at 11:22 AM on January 4, 2005

See here for some info. This happens to me when my cell is by my alarm clock as well. Even stranger, I heard it come from a police louspeaker yesterday when someone was standing by a squadcar. Kind of freaked a lot of people out.
posted by Ufez Jones at 11:27 AM on January 4, 2005

Perhaps it is similar to the noise discussed here?
posted by MrZero at 11:34 AM on January 4, 2005

Turn down your speakers and see if it goes away -- my guess is that's where it's coming from. If all the wires and bits in the audio system aren't well-shielded, you'll hear EM disturbances through the speakers.

If you think it's something mechanical, actually moving, I don't know.
posted by Wolfdog at 12:01 PM on January 4, 2005

Whenever a cell call comes in while my band is practicing, you'll hear a rhythmic clicking or buzzing over the amps, sort of like what an old-skool computer game sound effect of a pony's trot might sound like.
posted by sonofsamiam at 12:55 PM on January 4, 2005

Response by poster: Thanks for the suggestions, guys, but here's the weird thing: I don't have speakers.
posted by Specklet at 1:06 PM on January 4, 2005

Thanks for the suggestions, guys, but here's the weird thing: I don't have speakers.

Are you sure? Most PCs have a speaker in the back that makes a "beep" sound on boot up. They can be quite loud but were only ever really used by really old DOS games.
posted by bobo123 at 1:15 PM on January 4, 2005

Response by poster: Most PCs have a speaker in the back that makes a "beep" sound on boot up.

D'oh! Of course I have that! Foolish Specklet.

And I swear, this machine dates from the time of DOS games. O woe, why can't I work from home!
posted by Specklet at 1:41 PM on January 4, 2005

My cell does this as well when it's on my desk near the speakers. What you have is a crude aerial in there and it's picking up transmissions to and from your phone. My phone is GSM so sometimes I hear it when the phone is updating the time over the network, and I get about two seconds warning when it's going to ring - I hear the chatter before the ringer sounds.
posted by Dipsomaniac at 1:53 PM on January 4, 2005

I get the same thing on my car stereo if my phone is in the cubby hole below it and rings.
posted by Doohickie at 2:37 PM on January 4, 2005

sonofsamiam's "trotting" analogy is extremely apt. It was a funky little "ti-pi-ti, ti-pi-ti" beat. You could dance to it, if you wanted to (we needed entertainment at relay). I never realized this was so universal.
posted by Faint of Butt at 3:50 PM on January 4, 2005

Response by poster: Yeah, the old-skool digital trot is exactly what it sounds like...
posted by Specklet at 4:19 PM on January 4, 2005

I wonder if there's a difference in how mobile phones are shielded in different countries. Here in the UK, it's a well known phenomona. So much so, that if you're on a land line and that distinctive buzz sounds, the person on the other end will (sometimes) ask you if you want to get the other call.

My guess is that it's simply interference caused by having quite a powerful radio transmitter near wires connected to speakers. The radio waves cause induction cause the noise.

Some info here.
posted by seanyboy at 4:19 PM on January 4, 2005

I never realized this was so universal.

Yeah, the really bizarre thing is that it is the same for TDMA and GSM phones.
posted by oaf at 8:21 PM on January 4, 2005

It may be the spirit voices in your coffee maker.
posted by MotorNeuron at 9:39 PM on January 4, 2005

There used to be an ad on the radio that made that noise on purpose, I guess as an attention-getter. Drove me nuts. It really is a sound that most people recognise these days. My car stereo is the worst, mainly because that's the only amplified source that I put my phone near. My sister manages to always put her phone on our stereo at home and it freaks her out every damn time.

Apparently it shouldn't work without some form of amplifier, which those little midi speakers don't have (according to my geek hubby). Specklet, you don't have built-in speakers in your monitor?
posted by tracicle at 10:39 PM on January 4, 2005

This post explains it pretty well.

It's ubiquitous and pretty annoying - put a phone near a fairly long unshielded low-power audio line (i.e., antenna) connected to any kind of amplifying circuit and you can be fairly sure the speaker at the end of it will emit this pulsing noise when the phone is conducting any traffic with the cell in high-power mode. Even my Thinkpad, which is as shielded as can sanely be (most of the PCBs inside are protected by 3 or more layers of metal) receives this, apparently because of the unshielded parts leading to the audio jacks.

The only solution is to either move the phone further away or buy a better-shielded component. Or cut the wires from the speaker in question :)
posted by azazello at 2:08 AM on January 5, 2005

For what it's worth, oaf, I never heard that interference from my old TDMA phone. On the other hand, GSM and TDMA are very similar in terms of the transmission protocol (GSM is built upon TDMA as far as I know).
posted by azazello at 2:13 AM on January 5, 2005