arusr:
The wireless module is on a 3.3V regulator, and the Arduino I/O itself is on 3.3V I/O, so I'm not hurting the wireless module that way. But the ultrasonic sensor is on a separate 5V regulator...so it's sending 5V to the Arduino I/O...is this sending 5V to the wireless module somehow?.
Yes, it could be sending 5V to the module.
Reason: Arduino I/O pins have protection diodes on them. If you apply a voltage higher then Vcc to a pin it will go down the diode into Vcc, possibly raising the voltage coming out of other pins.
You need to put a resistor divider on the outputs of the ultrasonic sensor to drop it to 3.3V.