In an electric fireplace there are a few parts that move. If there is little or no background noise and you listen carefully, this can be noticed. If an electric built-in fire is built into a hollow space without sound insulation, this sound can be amplified.
To make your fire quieter, you can apply some insulation material (B) under the mirroraxis motor (A).
Move the mirroraxis (C) away from the motor as much as possible, this also makes a difference in the transmission of resonance.
A: Mirroraxis motor
B: Insulation material
Is there a clear sound for everyone to hear? Continue with the debugging.