i read somewhere (cant for the life of me remember where), that if you plug in and unplug your RCA's at your head unit or amp while the unit is on, you run a high risk of doing the RCA ground track or whatever its called, hence why they begin to pick up engine noise, as their ground is blown. (most common on the pioneers, coz they have a week ground track or something like that) hence pioneers being the most problematic.
if this is the case, that would be the source of my engine noise, and also the reason that its apparent now and not before when i had my old sub and speakers. only started happening when i changed sub/speakers, and when i was playing around with it i disconnected RCA's while it was on.
anyone know anything about this?