I'm trying to control the speed of a walkman motor with PWM from the Arduino board. It works all right, but i have this super anoying ca. 400 Hz tone disturbing everything.
The tone is obviously coming from the Arduino board, and it doesen't change when i change the PWM.
Even if i disconnect the PWM pin from the motor driving circuit, leaving only the ground connected i can still hear the tone faintly in the background.
If i reset the board the tone dissapers, but comes again at the same time as the sketch starts running on the Arduino board. But it is gone in the few seconds i takes from rest to the sketch is running (old Atmega 8 board).
I tried powering the Arduino board both from USB and external PS. without any difference.
Does anybody have an ide to the cause of this tone ?