BTW, Nuke used to install car audio professionally, his family owned a shop here in the PHX area. He has done all the installs w/ me on my vehicles. I have a ground thumping system in my 'vette that he and I installed. It developed some ignition noise... we finally narrowed it down to a bad coil.
If you haven't tuned up your vehicle in a while, now is a good time. Old ignintion parts can cause spark noise regardless of how solid your install is.
Good luck!