A loud bathroom exhaust fan usually signals dirt buildup, loose parts (housing, motor, blades, ductwork), or worn-out bearings, often identified by rattling (loose parts/duct), grinding (blade rubbing/bad bearing), or humming (motor/electrical issue). To fix, first, shut off power, then clean dust from the grille, blades, and motor with a brush/vacuum; if noise continues, check and tighten mounting screws, secure loose ductwork (maybe add insulation), and try oiling motor bearings with light machine oil (like 3-in-1) before considering replacement, especially if the fan is old (10+ years) or ineffective