Studio Monitor Tweeters are Buzzing Loudly out of Nowhere

I have a set of Samson Resolve 50a's running through an Alesis i04. Same setup for years now, but on Friday my tweeters started buzzing so loudly that they have become unusable. This happens even when there is no patch cord hooked up, and happens in every room in my house, even when not hooked up to anything. Also, other sets of speakers all still work fine through the i04. I thought it was a ground loop issue, or a failing patch cord, or maybe my interface, but it has to be the monitors. Anybody seen this before? Why would they both go out at the same time?

Both of them have the same fault?

Yeah, it happened at the same time to both of them while I was out. I came back and they were buzzing so loud I could hear them across the house.

Weird, they both have separate amplifiers per speaker (if I am looking at the right product pictures). Any possible evidence of any nasty power cuts during this time?

Yeah, they are separately powered. I wondered if maybe a power cut or surge affected them but I didn't really see any evidence - the clocks were all still correct for example. I was gone all day though, so I can't say for sure.

well that'll teach you to go out and leave your monitors on their own! very odd and very unlikely, but not impossible, that the same capacitor [or whatever] would fail in them both at the same time but .... not impossible..... have you taken them to some other location than your house to see if they do it there?

Yeah, same results in several rooms and even the porch.

well more than likely that covers it BUT I was thinking about trying them at some other house... just to eliminate the odd chance that it is something coming into your house circut that only the electronics in those speaker are sensitive to... admittedly it is a rare possibility

I might ask the neighbors when they are home. I guess today I will take them apart and see if a capacitor went bad simultaneously in both of them somehow.

Well, the capacitors don't look blown but I can't check them because my multimeter is suddenly missing. I'm going to order some new ones and cross my fingers that replacements will fix them.