There's no FCC rule about listening to HAM radio witout a license, or all scanners would be illegal. In fact, I had an old Kenwood TM-281 that I bought as a backup to later find out it wouldnt transmit at all: bad finals. Kenwood wanted $85 just to look at it, plus shipping both ways made that the cost of just buying another one. I plugged in a 1/4w whip, soldered some alligator clips to the power leads and gave it to my 16y/o nephew who uses it to this day to scan HAM repeaters for fun. It won't transmit, so I kept the handset as a spare for my mobile in the LandCruiser. He loves it.
Speaking of power hookups, most mobile radios do just fine wired through the main fuseblock, but it adds a layer of complexity when you have to troubleshoot signal noise on the radio. This is why all the radio manufacturers tell you to direct wire to the battery terminals, because they want you to get the best possible performance without having to call and bother them to learn you wired it into your alternator lead and have an audio tachometer!
More important is leading the power AND antenna cabling as far away from other sources of current as possible. Shielding only goes so far, but if you find an untraced noise in your mobile, a power filter (*just a set of matched capacitors to soak up the signal spikes) can be had cheaply and are very effective.