The other day I had a trip up North Jersey, and stopped by Musicteck (you can actually make an appointment with them). Too funny but he asked me to take a listen to some LP6k. I guess it was yours since Andrew asked me if I'm hearing any noise from single ended output
I tried that LP6k both with my U18t and Andromeda, even lowered the volume, and absolutely nothing, pure black background, no high pitch noise or any kind of noise, the sound was clean.
When you say "high pitched noise", which IEM and what cable? Honestly, I'm puzzled by this.