GoldWave (shareware)
LAME (freeware)
WinAmp (shareware)
GoldWave has a built-in function-generator that you can use to make a square wave of a specific frequency, then use LAME to encode it into an MP3 and play it on WinAmp to a decent amplifier that will send the signal to the sensor input of the PSOM, and use the volume control to slowly bring the amplitude of the signal up to the point that the PSOM detects it. I think I was using ~1300 Hz in that pic.

I think it IS the tone ring. When the guy bent the teeth back, he couldn't have gotten them perfectly aligned, and they were probably mashed flat, anyway. That means they aren't producing the same signal as the other 106 teeth, so every time the ring goes around, the ABS & speedo think the tires are coming to a dead stop for a millisecond.

There's only one tone ring for the 8.8" axle, and it has 108 teeth. It can be changed without removing the ring gear from the carrier, but the diff carrier has to come out of the axle.