K1NRG

Ground doesn't matter - like I said, I can get really loud noise in the Infotainment System using my HT with a TX on UHF and the HT antenna anywhere near the dash, point it toward the back window and noise goes away.

2015 GMC Sierra LTZ with factory Nav (full Infotainment System) with Bluetooth, Onstar, etc. Just installed a Yaesu FTM-400XD using a Comet NMO antenna mounted on rear edge of hood. When I TX on any UHF freq with any radio (mobile or HT) I get a loud thrashing sound that pulsates through all speakers. VHF TX is quiet as a mouse. RX is also normal on both VHF and UHF. The sound is coming through the system and not just the speakers directly as there is no sound when the System is powered off. If I hold my HT (BTech DRM-6X2) antenna (Nagoya 771) right over the middle of the dash (where the radio head is) and TX on UHF the system SCREAMS - if I hold it pointing out the rear window noise is almost gone and increases as I bring the antenna back to the dash. So there is something in the Infotainment system that is super sensitive to UHF. I tried a 19" mag mount antenna for the Yaesu and with it mounted forward on the roof (directly over the dash) I get noise (but not as bad as the NMO on the hood) which decreases to just a little when all the way back near the rear window (extended cab). The Comet NMO mounted on the rear edge of the hood is pretty close to the dash. There are a couple of YT videos of Sierra owners showing off their HAM Radio installs and one has same antenna mounted on hood no issues. I can't believe GM would have a radio head unit that is so sensitive to UHF considering how many Sierras probably have commercial UHF radios installed. Perhaps it's just my particular unit but I have had no other issues with the truck and especially the Infotainment System. Anyone else have issues with UHF and their Infotainment System?