Of the 3 units I purchased, 2 of them exhibit the annoying chirping sound.

 Exhibiting the same annoying chirping sound every few seconds that others have mentioned.

so I decided to contact APC customer service directly to let them know that I received a defective-chirping UPS, and they took care of me 100

I wanted to purchase from Amazon as they offered a great price on this APC BR1500MS unit, so I ordered the unit knowing that 'older' manufactured units had the annoying chirping sound, but hoping that I would be getting a newer-manufactured unit without the defect

The unit looks and feels very nice, but this chirping is so distracting that I can't use it right now.

As others have indicated, this unit has a rather atrocious constant high-pitched whine that periodically (once every few seconds or so) ramps up into a louder "chirp"

Attached is a video of the chirp squeal whine whatever you want to call it.

Random subtle chirps or squeaking is really annoying.

"chirping" noise every 30 seconds

I experience the "chirp" that the other folks that left reviews are also experiencing (included video)I purchased 2 units 1500VA and one 1000VA both experience the wonderful chirp that is a little annoying when they are together.very dissatisfied with both of these products as i've owned other APC units that run completely silent until under commercial power loss.*added to

The chirping is a real problem.

There is an annoying chirp that others have noted.

I'm sure that at this point, whether or not you receive a defective chirping unit or not depends on the Amazon warehouse that is shipping your unit to you

The next two units fail it's automatic self tests, goes into a fast chirp warning, and needs to be manually tested (HOLD power button for 6 seconds) to clear the error, this happens every 14-40 days

Sadly, my unit exhibits the "chirping" that others have mentioned, and whoa is it annoying as I can hear it over the fans of my desktop computer tower

These machines also have state of art computer controls that require clean a/c current

My inverter just doesn't have enough power by itself or clean a/c

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

Not as bad as I first thought