so ive been working on this install for like three weekends now and i thought i finally had everything sorted out but when i key up on 2m i get this really annoying buzzing noise that seems to change pitch with the engine RPM. its not terrible but its definitely there and its driving me crazy because everything else about the install came out really clean.

the radio is mounted under the passenger seat, antenna is a Comet CA-2x4SR on a mag mount for now until i drill the roof hole which im still working up the courage to do. feedline is LMR-400 running along the passenger side door sill. i grounded the radio chassis to the seat bolt and ran a separate ground to the battery.

on UHF its way less noticeable but on 2m SSB it really shows up. i didnt bond the hood or anything yet, is that probably the issue? or could it be the alternator? ive read so much conflicting stuff online i dont even know where to start troubleshooting at this point.

that RPM-varying buzz is almost certainly your alternator. classic symptom. the good news is its usually pretty fixable. first thing i'd try before anything else is an inline noise filter on the power lead right at the radio — Astatic and a few others make decent ones and they're cheap enough to just try. also check that your power leads are going directly to the battery and not to some distribution block or fuse panel under the hood because picking up noise from other circuits is super common.

the hood bonding strap can help too but i'd do the power supply stuff first since thats usually where alternator whine comes in. and honestly the mag mount situation might be making things worse since you dont have a great RF ground through the vehicle body. once you do the permanent mount with a good ground plane you might find a lot of it cleans up on its own. the 857d is a great radio in a mobile setup once you get the noise situation sorted, worth the effort for sure.

yeah i had almost the exact same thing when i put a radio in my jeep last year. turned out for me it was the ground wire — i thought the seat bolt was fine but apparently there was some paint or coating under there that was killing the connection. ran a dedicated ground strap straight to the chassis sheet metal with a star washer to bite through any coating and it made a huge difference. still had a tiny bit of noise but nothing that bothered anyone on the other end.

also just curious, are you running the radio off a fused direct connection to the battery or through the truck's existing wiring? that matters a lot more than people think