Just to clarify, you grounded the "matchbox" part? And it didn't clear
up the noise? If so then that might be the best you can do. I would
focus on noise from some appliance in your house.

Yeah, I don't have the matchbox mounted yet, but I've grounded it to
all sorts of places, and no change.

You're a genius tho, I solved my "powerline" noise problem at home! I
isolated the problem to a compact fluorescent lamp. Turn it off, S0,
turn it on, S3. My truck is 40 feet from the light too!!!! Have to
chuck this thing in the garbage.

As close to the fuel pump as possible. Just throw down a tarp. It's
worth the effort. You could also try using coax for the power line
from your battery (and grounding the shield), but that doesn't always
work.

Powerline for the fuel pump or the radio? That's a good idea for the
fuel pump, never thought about it. Radio... I question whether or not
the noise is coming from the radios power source.

I worked at a radio shop in Albany in the late '80's and drove through
Portland on occasion when they were building all those highways......
gawd what a mess!!! One time it took me two hours to drive just two
miles! I hope it's improved since then.....

Doesn't take 2 hours to drive 2 miles, but it can. Usually an hour for
20 minutes... They designed the interchanges stupider than crap, and so
those eat up 50%+ of your time at near idle speeds.