so ive been running my FT-7900R in my F-150 for about three weeks now and overall its been great but im having a real headache with antenna placement. right now i have a NMO mount on the roof toward the back and reception is fine but everytime i key up on 70cm i get this weird buzz coming through the truck speakers. not terrible but annoying enough that my wife is ready to throw the whole radio out the window

i ran the coax down the driver side door jamb and the power leads from the battery through the firewall on the passenger side. ground is on a bolt near the fusebox. someone at the club told me maybe its a ground loop issue but honestly im not sure i fully understand what that means in this context. anyone dealt with this before? is it worth trying a different ground point or should i be looking at ferrite chokes on the audio lines or something

yeah that buzzing through the car stereo is super common, almost everyone deals with it at some point. the ground loop thing your club buddy mentioned is probably right. what usually works for me is adding a ferrite choke on the RCA or speaker leads going to the head unit - just clip a snap-on ferrite right near the head unit itself. also worth checking if your radio power ground and the car stereo ground are going to the same point or really close chassis points, sometimes just running a dedicated ground strap between the two chassis grounds clears it right up.

also double check that your coax shield is actually grounded well at the NMO mount. a loose connection there can cause all kinds of RF getting into weird places. i had almost the exact same setup in a Tacoma years ago and it turned out the NMO mount was barely making contact with the roof skin because i hadnt torqued it down enough. felt dumb when i figured it out but hey

might also just be RF getting into the audio system directly if your antenna is close to the stereo antenna. i moved my NMO to the front of the roof on my jeep and it got way better, not sure if thats your situation though. the FT-7900 puts out a decent amount on UHF and it can find its way into stuff