check out the radio works mix 31 ferrite split beads
1/4" and 1/2" diameters I think they run $2.00 and $4.00
they really work! they are made by fair-rite
machined nicely.
also chat with ICE they make assorted filters andmobile regulators and filters models 441,443,444
1-800-423-2666
they also have techy reports 1 page each on many topics see report #44 mobile noise elimination
happy hunting..be sure to share your solutions in thie forum
marty ka7gkn
ka7gkn@arrl.net