Jack it up and spin the wheels independently and listen close. If you can't pinpoint the culprit without braking turn on the truck and do the same thing but have some one kit the brakes for you after you spin each wheel independently. That should at least tell you which one is doing it.
If it's a front check pads and rotors, if they seem fine grease the bolts, clean the caliper and pads out with some brake cleaner and spray some white lithium grease in there. Might find a rock or something once you have it apart.
If it's a rear drum most likely it is bad springs, maybe something rubbing, or out of line like the parking brake arm or something. Pedros was making a clicking sound until it finally fell apart in the drum on his red truck. I would recommend just spraying it all out with brake cleaner, checking the shoes and drums, and lubing it all up with grease.
If you can't tell I've had some brake issues in the past as well LOL.
2010 Toyota Tacoma Access Cab 4x4 Auto V6
2000 Ford Ranger 2WD 2.5L & 1976 Ford F150 Supercab 2WD 302