Dude are you on crack?
There is alway power from your Battery to your Amp. Whether it is in use or not. As long as it is connect to a power source there is juice!
So therefore, yes you can get noise if your Power lines are right next to your RCA's(If you have cheep RCA's or Unshielded units!!! I recommend Streetwires.3.0 or better!!!
A VERY BIG AND NOTICABLE DIFFERENCE!!!!
As far as Power wires go. I also Recommend Streetwires 4guage. Nothing less from the Battery to the Fuse block. Then maybe 8 guage out of the Blocks. Alway use the same guage wire for everything. 4 guage from battery to Block, 4 guage Ground to block, 8 guage out of blocks to amps. Don't mix and match. I recommend Streetwires because they use Silver Braided Wire and have the least resistance.
Getting a scope is great. But, not everyone has access to one or even knows how to use it. So my way is the next best thing for beginners.
Just turn everything down then turn up th ehead unit until it clips, if it doesn't then turn it up to the best sounding volume. Then adjust your gain unit it starts to clip or until you get it to the max volume you will listen to then back off 1/8th turn. Gets you inthe ball park.