My seatbelt alarm goes on when i buckle after i start my truck. same with passenger

Is your air bag light burnt out or not working on the dash? I have heard this will cause the seat belt chime to activate. You have to replace the bulb.

Do you have the same problem if you buckle up before you start the car? If not the RCM (restraint control moduel) may only read the condition at startup. This was common in older vehicles where people would buckle up before starting, then afterwards unbuckle the belt to circumvent the system. Reading the owners manuel may give you a key to the problem.