Is the noise just below the drivers seat area on the frame?
How many miles on the truck?
OK, the problem is the ABS module has a internal short that is keeping the abs motor running. This is a common concern on these trucks. Under the hood near the battery is a black box that has the fuses located inside. Remove the large fuse that is for the ABS. The cover of the fuse box has a label on it to show you what fuses are what. It should be a large (maxie) fuse and should be 50 or 60 amp. Remove the fuse and reconnect the battery. You can drive the truck like this, you will have normal braking but no ABS brakes.
To repair this issue, you need a new ABS module. The dealer will charge $600 to $800 for this repair. You can remove the module and send it out to have it repaired for about $150. Here is a website that can help you with the repair of the module. You remove it and send it to them and they will repair it. The site also gives directions on how to remove it. Let me know if you have any more questions on this issue.