Although the answer could very well be in any of the replies already given, it would help if you were to post your schematic, and oscilloscope waveforms.
It is possible for the inductor to interact with other components as voltage is turned on and off. (Example, high voltage spikes if disconnected abruptly, ringing with a nearby capacitor, etc.) The effect often gets worse as you increase the power.
To narrow down the source of the problem, consider the substitution of manual control instead of the IC's control. If the problem stops, then your control IC probably is defective.