APC ES750 weird issue

[Anonymous user]

I have 2 APC ES750's in my studio, tonight one emitted a constant tone and the green on light flashed on and off a few times, this lasted maybe 10 seconds then about 5 seconds later my other APC ES750 did the same thing, odd thing is I had other things on and not connected to APC's or surge protectors but they didn't flash or turn off or act as if I had just had a power surge or act as if my power went out.

I thought maybe they were self testing and the reason they did it close to each other was because I did hook these up about 10 seconds apart but that was just my first idea on why this happened.

Do you guys have any idea why this would happen? I couldn't find anything on the support section on this.
Any help would be great!