sub humming

[gnehzekul]

i used the instructions in the main page to install a amp and 2 12"s. even when i set the gain down to the lowest there is a slight hum.
what do you guys think it is?

i used a line to RCA converter to connect the high level feed to the amp. I did not use the high input on the amp. i used this connector in the previous set up to get the feed off the back speakers.
does that matter?

also the sub does not seem to be hitting as hard as when they were in my other car

fosgate 800.2 and 2 12" HE2 in a 01 navi no dsp