so i've been running a Yaesu FTM-400 in my truck for about three months now and overall really happy with it but i've been going back and forth on where to mount the antenna. right now i have a NMO mount on the roof towards the rear and the SWR is fine, like 1.2:1 across most of 2m, but i keep reading stuff about center of roof being better for pattern and i'm kind of obsessed with this now even though realistically i'm just hitting local repeaters and doing some simplex.

the other thing is the coax run — i tucked it under the door seal and along the A pillar and it seems ok but there's a slight buzz on receive sometimes when the truck is moving. not sure if that's the coax routing or something with the ignition or alternator. doesnt happen when the engine is off. anybody dealt with that kind of noise before or is my routing probably the culprit

the buzz on receive while moving is almost certainly alternator whine getting in somewhere, especially if it changes pitch with engine RPM. classic symptom. first thing i'd check is whether your coax shield is making good contact all the way through — sometimes when you tuck coax under door seals it gets pinched or the outer jacket gets compromised a little and you get all kinds of weirdness. also worth making sure your radio's ground is going directly to chassis, like a short run to a bolt on the firewall or floor, not just relying on the mounting bracket or the power wires.

on the antenna placement thing, honestly for hitting repeaters and local simplex the difference between rear roof and center is going to be pretty marginal. you might get slightly better pattern centered but we're talking about situations where you're moving anyway so it kind of averages out. i wouldn't stress about moving the mount unless you enjoy doing the work for its own sake, which hey, some of us do.

I had almost the exact same buzz issue in my jeep when i first put in my 7300 — wait no that's HF. anyway similar deal with noise on VHF. turned out for me it was the dc power cable running too close to the ignition wiring. i rerouted it and most of the noise went away. might be worth trying a ferrite choke on the power leads too, i put one like right at the radio and it cleaned things up a lot. cheap fix to at least rule it out before you start pulling the coax back out