O.K. a few things. I am no expert but I know you should be using a 4 OHM with that 6 watt amp not 8 ohm. To use 8 ohm you need voltage booster. I have the feeling the strange noise you hear is because you don't have filters on those motors. If you look at HL stock motors you will see some small brown resistors on the motor terminals. Take them off and put them on your red motors and the sound should go away. also if you build little boxes around those speakers the sound will be much clearer and deeper than even this...
I am working on a sound set up for the Panther "A" that will have a DC to DC voltage booster. Going to test tomorrow night and will do some pics and video hopefully...
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"There are things in Russia which are not as they seem..."
Georgy Konstantinovich Zhukov
Too many tanks, not enough time....