does this only occurs when u use your DIY speaker cable?
is the speaker cable use create is using multiple cat5? how long the cable?
If IT ONLY HAPPEN with your DIY cable then the possibility is that...
1) your multiple twisted speaker cable have too high capacitance and create osilation
2) check your twisted cable, is there mix cable between positive and negative? (if u are using the twisted 27pair, u may mix them...i had done the mistake once)