Theres nothing to tell, the on pulse isn't what matters, its when it is off the voltage flows threw the chokes and kicks back at a resonate frequency of the circuit. Thats all I know. Get your chokes and put the vic back up on the test table.
I will however say, I got resonance with several different values of capacitors, 223j, 224j, both were low freq. it is very easy to get results with these caps. anyone that builds the pwm will find it. also, I controlled the voltage at the gate of the N channel fet. I ground the gate out threw a 100k pot, and I use a 690 ohm resister on pin 3 of the timer just before the ground out pot. I use a shunt diode. its all very basic.