so i've been running an HT clipped to my visor for like two years now and finally broke down and got a proper mobile rig, picked up a used Yaesu FTM-400 from a local ham who was upgrading. thing is beautiful but man the install has been a whole adventure.

got the power leads run direct to the battery which i know is the right way to do it, used 10 gauge wire with an inline fuse close to the battery. the radio seems happy. but im getting a weird buzzing noise that changes with engine RPM which i'm pretty sure is alternator whine. tried a noise filter inline on the power leads but it didnt seem to help much. the antenna is a nagoya NMO mount through the roof which i'm pretty happy with, got a decent ground plane at least.

also trying to figure out the best spot for the head unit vs the main body. right now the body is wedged under the passenger seat and the remote head is on a RAM mount on the dash. works okay but the cable between them is a bit of a rats nest still. anyone dealt with the alternator whine thing? is there something i'm missing or do i just need a better filter?

the alternator whine is almost always a grounding issue in my experience, not actually a power filter problem. where are you grounding the radio chassis? if its going to the body of the truck somewhere far from the battery that can cause all kinds of noise. best thing is to run a dedicated ground wire from the radio chassis back to the battery negative, same gauge as your positive lead. i fought this same thing in my jeep for months before someone finally told me to stop messing with filters and just fix the ground. fixed it in about 20 minutes after that.

also check that your coax shield is properly grounded at the antenna mount. a poorly grounded antenna can dump a lot of RF noise right into the audio path too. the NMO mounts are great but if theres paint between the mount and the metal you wont have a solid RF ground there.

nice score on the FTM-400, those are great radios. i have the same one in my car and love the APRS stuff built in. for the cable management between the body and head unit, i actually just took my time routing it through the dash cavity and it mostly disappears. takes a while to figure out where all the gaps are in the trim panels but its worth it when its done.

cant help much on the whine thing since i got lucky and mine was quiet from the start but the ground advice above sounds right from what ive read. good luck with it