Engine bearing noise is caused by deep vibration noise from the engine and is usually "rod impact", which is caused by extreme bearing wear or damage. If the rod bearings are worn or loose enough to produce dull, hammering noise. Sooner or later, one of the bearings will fail, and when it does, one of two things will happen: the bearing will grab and lock the engine, or it will try to grab and break the lever. Either way, your engine will suffer significant damage and must be overhauled or replaced.
Bearing noise is not uncommon in high-mileage engines and those that are neglected and do not have frequent oil and filter changes. It can also be caused by low oil pressure, use of too low viscosity oil, oil damage, grease or dirt in crankcases, wear of rings and/or cylinders with too much interbleed air (gasoline dilution and diluent oil), incorrect engine assembly (bearing too loose), loose or damaged connecting rod bolts, or misuse of driving.
Bearing wear can be checked by lowering the sump and inspecting the rod and main bearing. If the bearings are badly worn, damaged, or loose, it may take you some time to replace them. But if the bearings are badly worn or damaged, the crankshaft may have to be relaid - which means a complete engine overhaul or replacement.