Sudden extremely loud low-pitch buzz lasts for a second - happened randomly

Question

My iMac occasionally would produce a sudden and extremely loud buzz from the speaker which lasts for 1 second or less only. The tone of the buzz is like an electronic distortion, something you would hear if you have a nasty electronic feedback in a digital audio mixer, low - mid range frequency. It is extremely loud I thought I was gonna have a heart attack. It happened very randomly, usually once a month or even less. But for the last 2 weeks I have had 3 episodes of it and 2 of them consecutively. 1st episode happened when I clicked on the delete button while trying to delete a contact from my MSN list. I had iTune opened in the back but not playing anything at that moment. 2nd episode, I had RealPlayer playing in the back, iTune opened but not playing anything, my iPod was connected with the iMac. I was converting a wav file in iTune into mp3, as soon as it was done, the loud buzz happened. Before I could catch my breath, (still had the RealPlayer playing in the back, iTune on but not playing anything), I tried to open a new tab in Safari and as soon as the tab was created, that loud buzz happened again. I tried asking apple genius but they haven't heard of anything like that and they guess it's probably the internal speaker's problem which I doubt. Any suggestion?

Answer 1

In some older iMacs, and others, a power surge could make noise;
and by this 'surge' I also mean some internal power component
could have a problem and supplying occasionally higher power.
Does this computer run warm or hot? Not sure if there is an
audible alert of some kind built into it; but a temperature widget
could be helpful to see how warm it gets. iStat Pro is good.
There may likely be a hardware cause behind this odd noise; so
I suggest you make an external backup of your work and files
just in case something else goes wrong; so you won't lose stuff.
Some kinds of backup include saving what you can to an off-
computer archive (DVD or CD media) to include using a bootable
externally enclosed FireWire hard disk drive; properly prepared,
and use it to make a complete computer drive 'clone' of everything.
A clone utility, such as Bombich's Carbon Copy Cloner, is good;
since it gives you some options and also the web page allows
you to get the utility and run it, the product is donationware and
is a good product. Also, in the header of the home page, you can
mouse-over the menu icons and see additional information.
In some older Macs with a loud buzz sound, there were some
significant hardware issues behind it. If your computer no longer
has any AppleCare protection plan left, this may be costly to fix.
Or you may luck out and the problem may be a loose wire, etc.
But to backup the files and stuff (and figure out how, in the case
of making only copies of iTunes libraries or iPhoto libraries) is
about the best immediate advice. The computer probably should
see a real qualified technician; not just five-minute duration 'genius.'
With a known pattern or set of events in which the computer will
make a loud and unnatural noise, a technician should be able to
duplicate it. And take notes to keep a small log of what all you do
when the computer makes this noise; so it may be duplicated in
the presence of a troubleshooting technician.
There may be some other cause of the 'buzz' such as a failing
optical drive or some circuit; and there also is a chance the
hard disk drive may be the source of odd sounds if it is failing.
(How loud are the fans in this computer? - Do they run alot?)
Not sure what else to say; but if the computer contents are
backed up, and the unit goes into the shop, you will at least
have a complete copy (bootable is best, on a FireWire drive)
in the form of a clone; that also could be used to troubleshoot
the computer or be useful in routine home/tech maintenance.
Good luck & happy computing!