Many older cars/trucks have a fuel pump in the gas/diesel tank that emits RFI through the external gauge connections. The simplest solution is multiple ferrite beads on the fuel pump connection wires outside of the fuel pump. You may need to lift the car/truck to gain access to these wires. Use two FSB31-1/2 snap on beads on each wire (usually 2 or 3 wires depending on make/model). Works on boat fuel pumps also.
Also make sure you connect a good RF ground to the transceiver ground post.
Note to Flex Radio users: Use snap on ferrites for firewire cable, speaker cable and mic cable, Ring ferrites for Antenna output and DC power.
For additional RFI suppression, use a feed line choke at the antenna to suppress common current on the coax feed line – see our store for feed line choke alternatives for use at the antenna.
If you use a linear amplifier we have RFI kits for linear amplifiers that help suppress RFI in your shack or in your neighbor’s house.