Is there any sort of noise typical of a precup burrowing it's way to freedom?
A long passed 1.6 GTD of mine, developed almost overnight a horrendous "clackclackclack,etc" from one cylinder, which wasn't due to fuel, or valves, didn't vary with load, not heavy enough for a big end. I always assumed it was a failing piston, or little end, but compressions with turning the engine by hand were reasonably even. Well no big hole in the piston at least.
It carried on like that, not getting worse, for some 10,000 odd miles before it ate it's oil and the Missus drove it, ignoring the idiot proof flashing red light and alarm.
She asks me, "Is it supposed to do that?"
I ask "How long has it been doing that?
She says "Oh, about 30 miles"
Sigh.
The car has been manhole cover lids for about eight years now, but I still wonder what that noise was?