2012 Prius V Driver Side Mirror Vibrating

Okay, so the Prius has picked up a vibration in the mirror/glass on the driver side rearview. The faster you go, the more it vibrates. I ordered what was labeled as an OEM replacement assembly, installed it, and had the same result. The new one was not TRULY OEM, so I put the old one back on, and still . . . vibrations. The passenger side mirror is rock solid.

When you push on the mirror/glass in the assembly it feels solid. Not loose or anything like that. You can push on it to adjust the tilt through the clicks with no issues. The assembly itself is on nice and tight, as I just remounted it.

So I know the issue is not in the mirror assembly, or I was issued a new assembly that had the EXACT same issue as the old one. I am not sure that is the case. It seems that I have a vibration coming from somewhere else, on the drivers side, that isn't resonating all the way over to the passenger side. I took the front left wheel off, remounted it, inspected and greased the front left strut. I'm out of ideas and wondering if anyone else has seen this and knows what the solution might be? Thanks in advance.