Can't stand Carey but no doubt it was a technical glitch (but not sabotage) that caused this. 

Funniest  I ever witnessed was Calgary gal Jann Arden's absolute (non-lipsynched at least)  off key butchering of the Canadian national anthem a decade or so back at a Flames game  - same issue, earpiece feedback failure. Felt bad for Jann, nice lady but yikes what a rendering that was.

Never have understood why people would pay mega bucks, stand around like penned cattle for hours in often inclement weather, to watch a performer fake, i.e. lipsynch, their way through a song.