Passat with grinding/static noise at 30-45 mph

I’ve spent about a $1000 fixing this thing and I haven’t even had to change the oil yet!

Its a 96 VW Passat GLX wagon with 140,000 miles my mom gave to me, and at around 35-40 mph, I hear a static-y grind-y noise, and there’s no agreement among the people I ask to listen about where it comes from exactly. It is not affected by acceleration, braking, coasting or the gear I am in. I even turned the engine off and heard it while coasting (relief!).

I assumed it was related to the grinding noise of the rear wheel bearings for a while. It started after they had been grinding for a while. I changed out the rear bearings and 1 stub axle/spindle myself, and the noise continues!

I also thought it could be air rushing through a gap somewhere but could find none in the gaskets surrounding the doors and hatch.

Anybody have an idea what this might be?