Occasional single esc beeping

Hey everyone! We are banging our heads on the wall trying to figure this issue out. So far, it has not been reproducible on command, which is the most frustrating part.

We have been flying this hardware setup for 6+ months on 20+ drones without ever seeing the issue.

Tmotor P60 170kv motors, alpha 80A hv escs, cube orange.

Our safety switch is disabled, so as soon as the cube boots, escs initialize…that is except for one…on rare occasion. Servo 4 starts beeping intermittently as if it is shorted, or not achieved its min pwm. This is where the rabbit hole begins…

First, we tried esc calibrations. It worked for a flight or 2, then back to the same problem. We then probed our servo rail, ran a known good esc on a load tester, and compared it with the problem esc, no difference.

Next, we swapped the problem boom arm with a known good one. Upon powering, servo 4 again, started beeping.

Next, i replaced the entire carrier board, suspicious of the servo rail. First boot, everything initialized properly. Great! I went out to remaiden it, but upon the second boot, the esc on servo 4 began beeping after initialization. Not to the normal rhythm, but this same intermittent one, as if its initializing then deinitializing.

I depowered (should have left it powered in the failed state) rushed back to the lab to have the EE’s probe it, but now am completely unable to reproduce it…after 50+ boot cycles.

I have a very strict deadline, so any help or insight would be huge.

My only options left (that i know of) from least tedious to most are:

Move the signal wire to the servo rail on the other side of the board
Swap out the cube
Swap out pbd/logic

Am i missing something?