I have a furnace Beckett Model "afg" series oil burner that just started today very loud rumble when in it's burning series. If anybody knows the answer would appreciate the feedback as soon as can. Thanks

Sounds like it is tune up time. New nozzle,filter,clean pump screen, regap electrodes,check high voltage transformer,set/check pump pressure, adjust air over burner,inspect combustion chamber/fire box, and barometric damper to name just a few things that should be done on a tune up.