Just make sure you've got a good solid ground. Even with a solid ground though, sometimes interference from your fuel pump or spark plugs will travel back down the shield on your coax or down your power cord and cause interference. SSB will make existing white noise a little bit louder sometimes, but if it's crackling it's probably your spark plugs because your fuel pump will make a whining.
Besides making sure you've got a good solid ground, you could also try twisting your power cord so that it looks like a barber's pole, or picking up a snap on ferrite choke to snap around your coax. Ethernet cables have all the individual wires twisted around each other, hence the name "unshielded/shielded twisted pair". Twisting them around each other helps reduce interference and crosstalk, and I have found that twisting your power cord a little bit in this manner so that it sort of looks like a barber's pole can sometimes help a little with interference that may be coming down your power cord. They make noise filters for your power cord, which may or may not help. If the noise is following your power cord it might, but if it's traveling down the shield on your coax, you might need a snap on ferrite choke or something. The in-line coax noise filters, in my experience, kind of do the same thing as the built-in NB/ANL feature of your radio (basically run it through some capacitors to even out the spikes in the audio caused by interference), and when you double up your radio's NB/ANL with an in-line filter, it kind of muffles things up.
Also check all the other electrical connections on your vehicle. When I tow a trailer with my pickup truck that has a bad ground on the lights, I will hear a pop/crackling sound every time I hit a bump, so check to make sure all your bulbs and electrical connections are good and tight.