according to the tone() documentation using tone() interferes with PWM output:
Use of the tone() function will interfere with PWM output on pins 3 and 11 (on boards other than the Mega).
On my Arduino Micro it seems to interfere with PWM on pin 5. After using tone() the PWM does not seem to work anymore. If I use pin 3,9 instead everything works fine.
So can someone explain why that is happening and if there is a way to circumvent that?