Hello. When I use external crystals, I have a low frequency (2Hz) disturbance on PWM outputs. This disturbance also appear on SWDIO & SWCLK pins. But everything is ok with internal oscillator. The MCU is STM32f401RBT6. Thank you for your help.
The first image is PWM output when using internal oscillator & The second image is PWM output when using external crystal.