This can cause some interesting behavior with some power supplies, for example mine makes a strange electrical noise and my framerate in games severely degrades on battery power

I'm personally running a Thermaltake Smart Pro RGB on my main rig, and it didn't even hiccup or make funny noises when I tested it

I work in a smallish home-office and the noise this thing makes is intolerable AND to top it off is not returnable

It isn't horrible, but in a home, you don't want to hear this humming noise continuously.

It's a quiet noise, but unbearable in a quiet environment

I was using the iMac when the power went out and the iMac immediately started making the same loud, unpleasant, disturbing noise.

There is one major flaw with this APC, it makes an annoying noise every 4 seconds.

Mine was produced in February and produces no audible noise once charged

Update: the loud noise produced by its cooling fan finally subsided

It's a quiet noise, but unbearable in a quiet environment

I was a little concerned about other's reviews citing the smell and noise--I shouldn't have been

I also have the cyber power equivalent and would recommend to buy thatover the APC as it does not make annoying noises.

I've been using APC UPS Battery Backups for 17 years and plan on continuing that trend for however long I need one.-The 1st UPS Battery Backup item I received started making a hmuming or hissing noise that made me afraid of an electrical fire.

I was hesitant in purchasing this model due to the number of reports of the squealing/strange noises.

I was going to use it in my home office but the noise was too annoying so put this one down in the utility room for my cable, wifi, etc and used a different one in my office....

The noise it does make is not the obnoxious squeak many report but rather a barely audible mid pitched whine that is not audible to anyone in the house when more than four feet away

Sadly, I wound up with a defective unit making this annoying noise

The noise is loud enough be annoying in an office environment.

Other than the odd noise though, it works perfectly

Biggest issue I have is that it makes a humming noise when the LCD screen is on.

It has a loud clicking noise, but for me that is a non-issue

The noise is so faint a person has to be within 2 feet of the UPS to notice it

This noise is fine in the basement location where I'm using it on our propane boiler, but I couldn't use this Back-UPS upstairs in my home office.

The noise is very quiet, but just enough to hear it if you are sitting nearby

I had no problem with a smell or any noises emanating from the unit like older

The noise makes it pretty much unusable for desktop applications, and it is better relegated to a closet if you are that lucky.

HATE the high pitched whispy chrips noises every 5 seconds.

easy to install, hot swappable battery, leds don't glow if you don't wanna look at them, nasty line noise as measured by an oscilloscope, but silent operation

Other companies are certainly improving, but when it's critical I always go with APC.

Not as bad as I first thought