RepairPal Certified shops can diagnose and repair your 1996 Mazda B3000. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Whereas I cannot say for sure, I'd probably inspect inside the rear brake drums for concerns.
Strongly suggest a local technician listen to your concern. A trained and knowledgeable technician should be able to narrow down your concern quickly.