so anyway i finally got the ft-7900r mounted in my truck after like three weekends of messing around with it. runs off the battery directly with a fused line which i know is the right way to do it but man running that wire through the firewall was a pain. ended up using an existing grommet near the brake booster.

antenna is a tram 1185 on a mag mount for now just sitting on the roof. i know i know, NMO through the roof would be better but im renting so i dont want to drill holes in my truck. the mag mount seems ok, getting into the local 2m repeater about 12 miles away without any trouble, and i can hit a couple 70cm machines too.

my question is really about the audio. when im moving it sounds fine but when i stop at a light or something with the engine idling there's this faint whine that kind of changes with the RPMs. i googled it and i think its alternator noise but wanted to see if anyone here has dealt with it and what actually worked. ive seen people mention those ferrite chokes and also some kind of ground loop isolator but not sure which one to try first. the radio itself is grounded to a bolt under the dash.

Classic alternator whine, yeah. The first thing id check before buying anything is your grounding. A lot of the time that under-dash bolt isnt actually giving you a solid ground because of paint or corrosion between the bolt and the chassis. Try running a short heavy gauge wire directly to a bare metal spot and see if that clears it up. Saved me from buying a noise filter I didn't need on my old Icom.

If you do that and still have the problem, then look at a bonding strap between the engine block and the chassis — sometimes thats where the noise is sneaking in. The ferrite chokes can help on the DC power leads but in my experience they dont fix the root cause, they just kind of band-aid it. Ground loop isolator is more for audio accessories not really your transmit audio situation.

I had almost the exact same setup in my Tacoma last year, mag mount and everything. For me the whine turned out to be because the mag mount coax was running across the door seal and i guess it was picking up something from there, moved it to come in through the back window gap and it got a lot quieter. probably not your problem but worth checking the coax routing too just in case. hope you get it sorted, that 7900 is a solid radio for mobile use