I recently bought a GK MB200 combo. It's old but works and sounds great. A couple possible issues though: As soon as I plug it in I can hear it humming, even before I turn it on. Anyone know what this could be or if it's the beginning of a problem? My father in law (who knows nothing about bass amps) thought it might be a problem with the power supply in the amp, or just that this amp has a loud power supply. Secondly, the chorus effect doesn't seem to do much at all. Is this effect REALLY subtle (I can hear just a slight difference in tone), or is mine broken? Thanks in advance for any help!