Unfortunately cars which have been partially or wholly submerged in flood water, can sustain a lot of damage to the engine in the form of dirt or sand getting into the inside of the engine or waiting to be drawn in once an attempt is made to start the engine,..before CLEANING it out properly.
It only takes a small amount of dirt to be sucked up into the oil-filter,..cause the filter to clog,..then the bypass valve operates allowing the dirt to mix with the oil which is fed to the engine's bearings,...engine failure follows farly quickly.
Submerged engines must be stripped down and thoroughly cleaned. If your engine was not cleaned properly, then I'm afraid it may well be junk by now.
That noise is the engine's bearings hammering.
Your donk is burning the oil due ring and bore damage from the dirt,.. plus loose bearings cause an increase in oil consumption through increased oil-spray onto the cylinder walls in severe cases..
Be thankful the engine goes at all.
If it is a manual gearbox, the clutch has probably thrown in the claw,..if an automatic,..could be anything.
A cheap second-hand engine which has no sludge or other signs of problems would be the most economical way out.
Youre transmssion will also need attention, if it too was submerged....
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