Headset hum
"The Sennheiser HMEC 45 KA was great for me on the B737, A320, and A330. However, I am now flying a B757 & B767 that generates an increasingly annoying hum when I lean forward. I suspect the windshield heat or the old technology CRTs.
I am shopping for a new headset that does not have this hum issue."
Check with your engineers. The headset needs to be "impedance matched"
for your system. Also check shielding ground.