93 full size Blazer 350 throttle body

High miles on the engine? The knocking/clacking and low oil indicator show loss of oil pressure. Loss of oil pressure can be from a few things: internal oil pump leak, external oil pump leak (pickup shaft to pump), hung up relief valve, oil filter failure, and worn bearings / excessive bearing clearances. For now, try switching to a heavier straight weight oil, and see if pressure picks up. If it does the loss of pressure is likely one of the reasons listed above, if it drops further, then the cause may be a leak on the pick up side of the pump. Usually, good oil pressure at idle then a loss of pressure at hotter temps indicates excess bearing leakage.