High Frequency Buzz/Ring

[doug_hti]

I was finishing a mix on a larger session
During the mix I was running
5.3.1
48k 24 bit

plugins running
1176s
LA2As
Reverb One
Focusrite EQs
DPP-1
Digirack Delays
Maxim

There was 65+ tracks.
I had approximately 8 AUX submixes
and two additional master faders seperating the Vocals and Instruments.

I started hearing a not quite subtle high freq ring (maybe 12k-15k range). I thought there was some sort of internal feedback loop, but this was not the case. I then began muting tracks and found a couple tracks that when muted, the noise would go away. Then I muted a track, it stopped, I unmuted and it was gone.

A few minutes later it came back. I then went through different tracks and I could mute any ONE of about 4 or 5 of them to get the noise to go away, but would come back when unmuted. Then I opened up an 1176 in the insert and bypassed, the ring went away and did not come back when I took the bypass off.

Are there any explanations for this?
file corruption???

Thanks!