Back-Up Power...Yet Again ?

I've got a Tripp Lite APS 750 on my Harman Mag.
It may have been doing it for awhile but I was in the basement when the inverter transferred the other day.
I'm experiencing a "buzzing" noise from the blower motors, on stand by power.
I did check the outlet voltage and it is around 97 v . That check was with my old amprobe. ( non-RMS meter) Someone said to check first with an RMS meter ?
Does anyone else notice this on stand-by power ?

I know low voltage is no good but I'm not sure what is causing it. ( if the reading is right) My battery is charged, 13.5 volts.
Any help/comments are appreciated.
Thanks, Mossy Beard

Heres a thread with my experiences with backup power.

Building a TRUE Sinewave UPS for My DVC-500

Thanks, that's a good read.
I hate to throw the Tripp Lite over bank and start over...
It was supposed to do the job. I wish I could find out where the voltage drop is ?
I assuming that the low voltage will destroy the motors ?

Thx, Mossy Beard

it's Not voltage, it's Not a true sine wave output, mine does the same thing. But it's a cheap UPS, but works until I can get the generator online....runs about 10 mins or so. (Small batteries).

WNY,
Do you have a Tripp Lite and have the same symptoms ?
Then the buzzing/low valtage would cause no harm ?

Thanks, Mossy

The buzzing is from the inverter sending modified sine wave power. Electric motor like pure sine wave. If left long enough on modified sine wave it could damage the motors.

No, mine is an APC or something like that.
But, yes, if left run long enough, it could damage motors as per other posts. I have never gone over 15 mins or so