I am guessing you are using your rear speaker level inputs as leads?

If so yes this can happen. What kind of line output converter are you using or does your amp have speaker level inputs? Quality makes a difference and also how it is installed.

If not and you are using preamp outputs some how then you should make sure the wires are not near any power cables. For example if you have a power cable coming from the battery and a preamp output wire next to it the power cable will make your subs have a static sound.