Looper Shutdown with a rattle noise

[nymack66]

Hey guys,
I really need help now big time, I took the Boat out today all was working well, made one stop after a 1/2 hour run at 4 to 5000 RPM, it acted really weird and will not start acted like a dead battery.
Waited a few minutes and she fired right up.
Ran for another 1/2 hour trolling and WOT at times.
Around 4000 RPM when it suddenly started to die down with a loud rattling sound, I immediately shut it down.
I try to start it and its making a rattling sound like something is loose inside and it will not start, I did a compression check on the 1 and 3 cylinder both shows around 60 I am completely stump all the plugs looks ok well oiled it did not overheat since I saw it running at 140 degrees.