I'm with Renze, dont use it until you have checked all the main bearing caps and play in the big ends.
but before you pull it apart do some tests to try to work out which caps to start looking at.
1. if it is a rumble under load it points to Main bearings. (will also have very low oil pressure when hot, you cannot go by pressure if cold)
2. if it is a tap tap tap it could be gudgin pin, worst at high rpm and no load. and no loss of oil pressure
3. If it is a knock knock knock, from idle up to mid RPM under most load conditions it would point to Big End bearing. (this is most likely) and you will also have low oil pressure when hot.
To test 2 and 3 above to locate which cylinder it is before pulling the sump off.....
1. Hold a big screw driver (or similar) with the handle in your ear and the point end against the side of the block just above the sump flange (if possible) you will hear the knock knock loudest when in line with the effected CYL. give or take.
2. Loosen the injector pipe on running engine (fast idle) on the cylinder you suspect, and check for a change in the knocking or tapping (big end will be quieter with no
fuel , Gudgin may be louder with no fuel)
you should be able to determine which cylinder with some accuracy by this method before dropping the sump.
When draining the oil run it through a filter funnel and look for metal shavings (bits of bearing are non-magnetic)
if the oil is clean, it may be an easy fix, if the oil (or sump) is full of bits of metal then you will be in for a crank grind and complete set of new undersize bearings, and a new oil pump
with the sump off, first check play in the BE caps, starting with the one you determined above, if there is any play side to side or twisting remove the BE cap and check bearing and crankshaft condition (out of round limit is only 0.001", or 0.025mm) light surface scratching on the crank is ok, but it must be round!
Assuming Copper lead bearing shells are used by the factory, there should be no sign of copper showing through the thin layer of Lead (actually Lead-Indium alloy)
If there is no sign of play or ware in the BE look at the main bearings, first take off the main cap closest to where the noise was coming from, noting if the bolts are "tight"
Finally check the Torque on all cap bolts (as per setting in the
manual )
Good luck, hopefully it is just a loose bolt!
Steve