So I made multiple test drives on local roads. First, made one drive before opening up the dashcam to confirm problem still exists. In this recording, there was a lot of static noise for the 1st 10 seconds and then it cuts out immediately to a softer static noise background, but the recorded sound is very muffled and not normal. Here's a youtube video clip of this.
Afterwards, I opened up the dashcam and put some folded electrical tape under the microphone in hopes that it would stick to the top of the capacitor better. Here's a picture of the end result.
I had thought about moving the capacitor to the side of the case where the labeled mic opening is, but didn't want to risk breaking the microphone wires as it looked like it would need to be bended awkwardly to do so.
Then made a couple test drives and everything sounded fine so I was thinking the issue was fixed. Decided to make one more test drive and after about 1 minute of driving, the loud static noise came back and lasted for the remainder of the 5 minute drive.
Then made another test drive with the dashcam powered by a USB powerbank and there was no sound issue.
Switched back to using the car charger and for the first 4 minutes everything sounds fine. Then in about the last 15 seconds, the loud static noise comes back as the drive is about to end and I'm about to park. Here's a youtube clip where the static noise starts coming back around the 01:25 mark.
I ran out of time to do anymore testing.
Could any conclusions be made after all this? I want to test more with the dashcam powered by the USB powerbank as I only got one chance to try with it. Could the static noise really be caused by a bad cigarette power adapter cable?