2016 Nissan Titan XD electrical system problems

Good Afternoon, My brother was driving my Nissan Titan XD 5.0 Cummins Diesel from Naples, FL to Ft . Lauderdale FL , and the truck was running fine at around 70-80 mph with no issues .As soon as he proceeded to the exit in Lauderdale around 60mph, all of a sudden truck flashed all kinds of warning lights came on randomly and motor shut down . Smoke coming from starter and solenoid below the fuse box. He is an engineer for North Collier Fire and put out the flames immediately .

I'm having fed back through the speakers periodically. 2or3 times a month. With or without radio on. The driver (me ) move my left foot around this causes fed back/ static sound come over to radio. I've turned it in to nissan and they claim nothing is wrong. They've claimed to remove the seat to check for wires. Bolts were not touched?? Also claimed no wires under floor board.