so i've been running a ft-7900r in my truck for a few months now and the install has been kind of a mess until this weekend. finally got the control head mounted where i can actually see it without taking my eyes off the road too long, and the radio body is tucked under the passenger seat which cleans things up a lot. ran the power leads direct to the battery with an inline fuse which i probably should've done from the start instead of that whole fiasco with the accessory circuit.

antenna is a NMO mag mount on the roof for now, i know i know, not ideal for a permanent install but im renting the apartment so drilling isnt really an option at my place, and i dont want a big hole in the roof of the truck either. signal seems fine honestly, been hitting the local 146.820 repeater without any issues at about 15 miles out.

my question is about interference. i get this weird buzzing noise that kind of pulses with the engine rpm, worse when i first start up and then it sort of settles. ive heard this is alternator whine but wanted to see if anyone else dealt with it and what actually fixed it. ive seen the ferrite choke suggestion and also the in-line filter for the power leads. wondering which one to try first or if there's something else i should be checking.

yeah that's almost certainly alternator whine, the rpm-following thing is the dead giveaway. first thing i'd do before buying anything is check your ground. like actually check it - not just assume the chassis ground is good. run a dedicated ground wire from the radio chassis directly to the battery negative, same length or shorter than your positive lead, and see if that changes anything. a lot of times people run a nice clean positive to the battery and then just ground to whatever bolt is nearby and thats where the noise gets in. did that on my old chevy and the whine went away completely without any filters at all.

if the ground doesnt fix it then yeah a power line filter like the astatic or similar ones work pretty well. ferrite chokes on the mic and antenna feedline can help too but usually the noise is coming in on the power side not the rf side so start there. the mag mount itself shouldnt be causing you problems for what you're doing, dont let anyone give you too much grief about it.

I had the exact same issue in my Tacoma when I first put in my TM-V71A, drove me crazy for weeks. What ended up working for me was running a separate ground wire like the other reply mentioned but also making sure the coax shield was properly bonded. my mag mount was sitting on painted metal and i didnt realize how much that mattered for rf grounding. once i got that sorted with a small ground strap it made a noticeable difference on receive too, quieter all around.

the FT-7900 is a solid radio by the way, i had one as a base station for a while and always liked it. enjoy the mobile operating, there's something really nice about being able to check in to nets during the commute.