My unit has recently begun to click intermittently without any evidence that the AC incoming power is fluctuating or failing.  What gives?  

Also how do I run software on a Windows 10 platform that can diagnose whether the unit is in need of repair?  I couldn't find the particular model on the website listed in the software/firmware section of the Support pages.  In the past I have been able to give a previous model a health check, but it seems this one isn't supported any more.

Your BR800BLK UPS is capable of adjusting the AC line voltage without switching to the battery. It is capable of doing this for as long as necessary, but you might want to find out why the line voltage is too low or high.

There will be no indication of this happening on the UPS itself (other than the relay clicks). APC's PowerChute software would tell you if the problem lasts for more than a few seconds.

Many thanks.