Harmonic drone while driving

Started a few days ago. Seems to originate in the front passenger side. There's a slight noise at all speeds but around 40, 60 and 80 it seems to resonate.

-Shifting to neutral doesn't affect it.
-Hitting the brakes only affects it by slowing the car down out of the resonant zone.
-Rotated tires, no change.
-No lateral "play" in the wheels when I rotated the tires this morning.
-It seems like making turns at speed might have --some-- affect on it, but very slight. Slight enough that I could be imagining it. I haven't noticed a decrease in fuel economy.
-Tires are worn, although not down to the wear bars yet. Will be replaced at inspection.

It was mentioned that new brake pads would be in store during the last inspection. Front pads still have between 1/8" to 1/4" left. They also mentioned machining the rotors. That being said, the pads looked like they are riding on the rotors. Could this be causing the ringing I'm hearing? Probably unrelated, but a new front left strut is also in the works per last inspection.

Water pump, drive belt and coolant replaced at 78k per Toyota owner's site. (Bought it used at 100k)

Car is a 2006 with about 175k on it. Most recently replaced the cat with an aftermarket last fall. I'm due for a state inspection in September, but I commute 700 miles a week, 95% highway. Any guesses so I'll have an idea how much lighter my wallet is going to be?