If you are referring to the dinger for the key in the ignition, there are a couple ways to disable that. Some remove the wire from the ignition switch which allows reconnecting the wire when you sell the truck.

Many cut the black or dark gray wire with a pink tracer that is located on the steering column. I removed the lower dash cover, found the wire, cut it and taped off the ends.

There are many threads about this mod that give much more detailed instructions than these. Others will give more advice to do this.