so i've been running my FT-857D mobile for about three weeks now and overall pretty happy with how the install went, ran the power leads direct to the battery with 30amp inline fuse, mounted the head unit on a RAM mount on the dash and the main body is under the seat. antenna is a Tarheel screwdriver on a trailer ball hitch mount on the back of my Tacoma.

anyway the problem is at highway speeds i get this weird raspy kind of buzzing on receive, doesnt matter what band or frequency, its there whenever im going over like 55mph or so. at slower speeds its totally fine. my first thought was alternator whine but it doesnt really change pitch with the engine RPM, it kind of just... stays the same and disappears when i slow down. also it only happens on VHF and UHF, HF seems totally fine which is strange to me.

i havent done anything to shield the power leads or added any ferrite chokes yet, maybe thats the issue? or could it be something with the antenna feedline routing? i used LMR-400 which i thought would be good enough but now im second guessing everything. anybody dealt with something like this before

that's a weird one because you'd normally expect alternator whine on HF more than VHF but honestly it could still be RF interference from something aerodynamic lol. wild guess but have you checked if the noise is coming in through the antenna or if it's getting into the radio body itself? easy way to test is just disconnect the coax and see if the noise is still there on a dummy load or just the antenna port open. if it goes away then something on your truck is radiating and your antenna is picking it up at speed, could be wind buffeting on some plastic trim piece with a loose ground or even brake dust on a wheel sensor.

also worth checking your coax routing, if any of the LMR-400 is running close to ABS wires or near the transmission tunnel you might be picking up something that only kicks in at higher speeds when those systems are more active. ferrite chokes are worth throwing on anyway, they're cheap and sometimes fix stuff you didn't even know was broken.

i had almost the exact same thing on my old Silverado with a 2m/70cm mobile, drove me crazy for like two months. turned out to be my backup camera wiring of all things, it runs right along the headliner and i had routed my antenna feedline through the same general area and at highway speeds something about the vibration or maybe the camera staying active was putting noise right into the coax. once i rerouted the feedline down the B pillar and under the carpet instead it cleared right up. probably not your exact problem but the point is it was something totally dumb and non-obvious so dont overlook the weird stuff.