Kyler

I installed a "BESIGN Ground Loop Noise Isolator for Car Audio/Home Stereo System with 3.5mm Audio Cable" that I got from Amazon. In a quick test parked in the driveway there was no whine even with the car radio at its highest volume with the GMRS on. Here's a big thanks to everyone who responded! I'm very grateful. I've spent months trying research and fix this on my one. WRQC527 nailed it on the first go. I should have started here.

if the audio isolation transformer I ordered doesn't work, I'll try this. Thanks!

Thanks for the suggestions. I've read up on ground loops and decided to try the audio isolation transformer first. Thanks!

No whine when the cable is unplugged from the car. No idea what the impedance is nor how to measure that. I was assuming since my phone output worked that the GMRS would work the same way.

I plug my Midland MTX-275 external speaker output into my aftermarket (Dual Elect XDM280BT) radio aux input plug. I get a noticeable alternator whine. I get the whine with the GMRS turned on or off. I tried a shielded 3.5mm audio cable and that didn't help. I do not get the whine if I plug the car aux into my cell phone's 3.5mm output. I do not get the whine if I unplug the cable from the GMRS. I tried putting an Install Bay IBNF30 Noise Filter on the GMRS radio but that didn't change anything; still had the whine. Has anyone had the issue and does anyone else plug the GMRS into the car radio?