APC Back-UPS Pro 1500S Producing a Coil Whine-Like Squeal Without Load

[Anonymous user]

I have just purchased an APC Back-UPS Pro 1500S uninterruptable power supply from Amazon the other day, and I've found a peculiar issue with it.

Despite letting it to charge for almost a day, it produces a faint squeal still audible from about a meter away. This sound modulates between a lower and a higher pitch in a regular pattern.

This occurs even when the UPS has no load placed on it, and while it is plugged into a presumably good outlet.

• Is this an example of coil whine?
• Is this normal for this model of UPS, or is this unit defective?
• Is there a way to mitigate the sound without the need of hardware mods?
• Do all UPS's of this power level produce this sort of sound, or are there any pure sine wave 900w+ UPS's on the market that can operate silently?

Many thanks in advance for any advice y'all can give?