You should hear my lexus. It grinds like mad between 35-45, then it goes away. Wheel bearings check out, suspension is
tight.
I'm just waiting for a diff to blow or a CV to explode, but there is nothing externally wrong with them. So it's a waiting game.
Sometimes with older cars, once you've checked everything you can, what you need is a louder stereo.
That said, Malathion's vacuum lead is a great one to chase down, especially if you are losing heater performance under load.