I bought a Power noise filter from Walmart that wires inline with your power leads to the Radio. They are made for Car stereo systems so you'll find them in that department. I had to have this for my handheld to get the noise out of it. Something you could try before that is to have your radio on, squelch off and remove the coax and see if the noise(s) disappear. If they do the noise is most likely coming in through the antenna system, not the power leads. Normally these radios made for mobile have filtering (12 volt)built in . As far as Antenna "performance" Larson is a very good choice. Your vehicle roof should be MORE that enough ground plane for your antenna if it is mounted high enough so it can "see" metal beneath(most of) it.
Did you check SWR