This was a first for me today: 2008 G1000 172S Turned on the master prior to start and heard a *piercing* noise of what sounded like fragmented words of the AWOS leaking over onto the CTAF frequency (CTAF was currently in the active spot). Example: ".........WIND......AT 5........ALT.........02" only loud enough that I had to take my headset off. I immediately tried adjusting the volumes of both the COMM1 and COMM2 radios and that seemed to help the volume aspect, but there was still this broken leak of what sounded like the AWOS coming over. This was all apparent on COMM1 and I believe on COMM2 when I isolated that, but I can't be sure. It seemed no matter what combo, there would be some strange phantom "RX" that was creeping in. Here is a video of what I mean. I tuned COMM2 to 121.5 as there theoretically wouldn't be any radio chatter on that, but yet you can see the "RX" persistently popping up (looks like in sync with when the COMM1 awos is receiving). It also may just be in my head, but I thought I heard a much more apparent whining noise when taxiing out and running up (higher pitch with higher rpm). I know this is indicative of something off with the alternator and ground, but at the time wasn't sure and haven't had a chance to research it yet. This ultimately made me scrub the flight as I figured the COMM1 weirdness was potentially a symptom of a larger problem as evident by the alternator noise. In any case both an instructor and mechanic took a look and thought it was odd as well, but had to leave before I heard an actual diagnosis. Just curious if this stands out to anybody on here. Thanks!