LR,
You may wish to check out this website, created by a data recovery company, that contains samples of the many sounds they've seen hard drives make when in self destruct mode....
Failing hard drive sounds - Datacent.com - Datacent
P.S.
I achieve a visual aid to tell me which drive is going?
Is wishful thinking.... there will be a lot of background chatter going on that would make such a thing a pointless attempt as there would be almost continuous comms going on to both drives.