45 is an oxygen sensor. Passenger side.
The beep is definately the sensor on the transfer case shifter. You need to make sure the switch is repositioned to stop the noise. The beep comes when the transfer case is in neutral. So effectively the shifter is moved to the center to activate the switch.
http://www.robisonservice.com/servic...ouble.asp#1990
45 is the passenger side O2 sensor. If I'm wrong it's not of much consequence as you want to replace those in pairs anyway. Good news, is your gas mileage will go up with better functioning O2 sensors.
http://www.okierover.com/o2sensors.htm
