Why does my UPS click when I switch to Dashboard?

Question

I have a APC Back-UPS 750, which has worked well for me for several months with my old 21" iMac and various external devices (FW BD burner, FW hard drive, DSL router, speakers w sub). I recently switched to a Mac Mini and TD Display, leaving the other externals as-is. I immediately noticed the UPS clicking and popping, irregularly, every minute or so, sometimes more often, sometimes less. It sounds like something is switching on and off inside the UPS. There is no interruption in power to the devices.
Most bizarrely, I can predicably product the behavior by swicthing betweem the desktop and Dashboard. Sometimes I can even make the UPS click by moving a Finder window around rapidly enough.
Anyone have any ideas re: what's going on here? Googling led me to believe that perhaps I am overloading the UPS (a Mini + TD display does use more power than a 2006 21" iMac), but going through APCs product wizard leads them to suggest... the same product. Adding up all of the power reqs for my hardware does make it appear that the Back-UPS 750 should be big enough.
Thanks for any ideas. --Chris

Answer 1

While the clicking could be that you're overloading the UPS, I don't think it's that.  I have a client with a 27"
2011 iMac on a BackUPS750 and it's fine.
More likely is that you're losing AC power intermittently (brownout) or your mains wiring in the walls is having issues.  Corroded terminals or rats chewing on the wiring can cause your wiring to not be able to supply "full power" to the outlet.  I've had both cases at client's offices, where "everything was fine" but the new (more power hungry) computer would reboot spontaneously or the lights would dim briefly when the computer was turned on, etc.
Depending on when your wiring was installed, a few decades ago, aluminum wiring was used and can't handle the loads like copper wiring.  And a few decades ago, the way outlets were wired with the "quick push in" style (rather than using the screw to hold the wire) often is a problem.  I've had many sites that were renovated back in the 80's that much of the "push in" style outlets are intermittent.  Simply moving the wire to the side terminals on the same outlet would fix the issue.
So try plugging the UPS into a different physical outlet.  Ideally, you want the outlet on a different circuit breaker because if the issue is in the whole circuit, just moving to a different physical outlet on the same circuit will still have the same issue.  (If you get desparate, take your computer and UPS to a friend's house for a weekend.  Have a party while you're testing.  In fact, make it a gaming party. )  If moving the computer to ad different outlet/circuit/house "fixes" the clicking, then have an electrician check your outlets.