A bit off-topic, but maybe an electronics expert can help me with this.
My MorningStar TS-45 also buzzes like this, but at a higher frequency that most would term a "whine" varying from about 2-7 kHz (by my ear, but my musicianship has fallen by the wayside). Although it's not that loud, I find it annoying and because of that, when I build by own, I want to use a frequency in the range of 30-35 kHz (this coincides with the frequency I will be using for the buck converter).
My question is: does anyone know why the manufacturers choose a frequency this low, and why it would need to vary in frequency ? I don't think it's cost or efficiency; I can find MOSFETs for less than $2 US that switch fast enough that they're dissipating less than 2% at 100 kHz.
Any ideas ?
Dave