Fan controler problem

I have the vantec NXP-201 and it works just fine the only problem is when I turn the fans down it makes a crackling sound but when i turn them up again it is fine, is this normal.

Crackling is not good. Do you see any sparks? (eek!)

Keep an eye on your computer, my fan controller (Vantec 201) stopped working. I had to RMA it, but since I got it back it works perfectly.

It's the PWM causing your fans to pulse at high frequency. If the fan hub and blades are light then at low RPMs feeding it a pulsed waveform will cause it to growl/crackle as it speeds up/slows down by a tiny margin