Emits high pitched humming noise.

Awful high pitched whine right out of the box

I don't know if this is considered normal or not but this UPS makes a constant, loud, high pitched tone

But even when turned off makes a quiet low pitched squeal.

But it makes an unbearable high-pitched noise

Let's out a super high pitched barely perceptible whine/shriek

Switching to battery emits a lower toned buzzing (which is pretty standard), but when it turns back to AC online it emits a constant high pitch sound which hurts my ears.

About two months after ordering, the unit started making a terrible high-pitched, whining noise

Started making a horrible high-pitched whining sound a few days after my return window closed

Also, when plugged in, there was a high-pitched noise, very faint

, very loud, high pitched tone which would normally mean that the unit is on battery power - but my computer and everything else connected to the UPS (battery and surge only side) were completely dead the instant the lights flickered the first time

When fully charged, it has a faint, high pitched whine.

Awful high pitched whine right out of the box

It does not work -- I have taken t o the cleaner

t has been working for a few months without any probems