I hear it in lots of cuts. The more revealing I make the system, the more it stands out. (Like an upper frequency "hash.") Best I can tell is that it is either in the recording process or more likely, in the digital transfer. I’ve also noticed that some cymbols don’t fare so well in the digital transfer.
But, knowing it can be there, I’ve planned for it. I put a "TUBE" setting on the crossovers that puts a 3 mfd cap/20 ohm resistor in parallel with the Heils. This typically takes care of it without too much high frequency loss and provides a different experience.
Listened to Nora (YouTube to the rescue again) and there is definitely a "resonance" in her voice at that point that could easily interact with a speaker/room. I would have to listen "more intently" but there could be some "hash" in there too. Sometimes, a singer will get too close to the mic overloading it and the padding in the board is not set to account for it and you end up with distortion. Certainly lots of examples of that!
Sometimes, in extreme cases, the singer doesn’t even need to get near the mic for a distorted sound if the padding is off. I bet Eric cringes every time he hears this:
https://youtu.be/4-J41AdchlU?list=RD4-J41AdchlU
BTW, Listen to Eva Cassidy, Live at Blues Alley, and you may hear a few passages similar to what you heard from Nora.

