So on my brother's '06 Duramax Diesel, i put in a usa spec ipod adapter kit

at first he wanted to have it come accross his xm, so we cut the green wire down by his xm, but then when he realized he couldn't scroll through his music to select the song he said screw it and decided to do it the cd way... So i hooked the green wire back up and crimped it together, but now you can hear the motor. I taped my connection and everything. But you can still here the motor.

If i soldered the connection instead would it make any difference in getting rid of the motor noise? How do i get rid of the motor noise?