so after about three weekends of crawling around under my dashboard i finally got my FT-7900R mounted and running. power goes direct to the battery with a fuse about 6 inches from the positive terminal like everyone said to do, antenna is a Nagoya NA-771 on a mag mount on the roof for now until i figure out if i want to drill. overall im pretty happy with how it came out except for one thing.

the audio from the speaker is just terrible when im moving. like at a stop it sounds fine, clear enough, but once i get moving above maybe 30 mph theres this low hum that gets worse the faster i go and honestly its pretty hard to hear people talking over it. ive tried moving the radio around a bit, checked that all the grounds seem tight. not sure if its the alternator or road noise or what. anyone dealt with this before? also does the mounting position of the control head matter for this kind of thing?

sounds like classic alternator whine to me. the frequency it changes with engine speed is kind of the dead giveaway. what you want to try first is getting a noise filter — sometimes called an inline noise suppressor — and putting it on the power lead. the little ones from West Mountain Radio or even the cheap ones off Amazon actually work pretty well for this. also double check where your power cable is running because if it's anywhere near the ignition wiring or the firewall grommet area it can pick up all kinds of garbage.

the other thing and this is something people dont always think about is your audio ground. if the radio chassis isnt properly grounded to the vehicle body you can get a ground loop which sounds a lot like what you're describing. try running a short braided strap from the radio chassis directly to a nearby chassis bolt and see if that changes anything. mag mount antennas can also be a factor but usually that shows up more as RF getting into the audio than a hum per se.

oh man i had the exact same thing with my 7100 when i first installed it. turned out the power cable was zip tied right next to a bunch of the car's computer wiring behind the glove box and that was causing problems. i just rerouted it further away and most of the hum went away. still had a tiny bit left and ended up getting one of those ferrite chokes and clamping it on the power leads close to the radio and that finished it off. took me forever to figure it out but once i did it was totally fine. good luck with yours, mobile installs are always kind of an adventure