Originally Posted by North_of_49
If it's the tone I'm thinking of... it's just the servos. Try gently tugging the elevator or rudder pushrod and I bet it goes away. It's normal though.
I am familiar with noisy servos from various helicopters. This is not the servos. This is coming from the ESC as it is a continuous tonal beat, not a chattering like you'd hear from servos.