So i've been running a Yaesu FTM-400 in my truck for about 3 months now and the TX side of things is great, people say the audio sounds clean and i'm getting into all the local repeaters no problem. But man the receive is driving me nuts. There's this kind of buzzy hash noise that follows the engine RPM — like it goes up and down with the throttle. It's worse on UHF than VHF for some reason.

I ran the power leads direct to the battery with an inline fuse and everything, the antenna is a NMO mount on the roof. The coax is RG-58 that came with the antenna kit. I dunno if thats the issue or if its something with the alternator. Truck is a 2019 F150 if that matters. Anyone dealt with this before?

Classic alternator whine, had the same thing in my Tacoma a few years back. The RG-58 might be part of it honestly, that stuff isn't great for mobile use — the shielding isn't as tight as LMR-400 or even LMR-240 and it can pick up all kinds of noise. But the bigger thing to check is whether your coax shield is actually bonded to the vehicle chassis properly at the antenna mount. If the NMO mount is going through the roof and the ground path back isn't solid, you're basically running a loop antenna for all that ignition and alternator garbage.

Also worth throwing a ferrite choke on the power leads right where they enter the radio. Like a big clamp-on type, wrap the wire through it a few times if you can. That cleaned up probably 80% of my noise issues. The other thing people dont always think about is grounding the radio chassis itself to the car body with a short braided strap, not just relying on the negative power lead to do that job.

yeah the RPM-following noise is almost always alternator. i chased that same thing for weeks in my old chevy. ended up being a bad ground on the antenna mount, took me forever to figure out because everything looked fine visually but when i actually cleaned the contact point under the mount and used a star washer to bite into the metal it went away almost completely.

also on the RG-58 thing, i'd swap that out if you can, just not worth using on UHF especially. you lose more signal than you'd think on a longer run even at 440.