I exprenced the same thing. But the oil level did the opposite.I had the same tapping sounds i woul run an oil addative through it. It would help for a while then start again.Then later the check engine light came on. It had over 100k on it so i just figured it was a milage thing a few days later my wife was driving to work and oil light came on.I checked the oil it was way high on the stick.Which i knew was wrong cause i just changed the oil my self and left it a quart low.So i pulled it home pulled the oil plug and it has brass shavings in the oil.The engine want even run it cranks but jumps around and want idle.I am planning to replace the engine but pay someone.I do shade tree work on my own stuff but the motor comes out the bottom and thats just to much for me.Accadents cost money.If something sliped and got hurt i couldint work no work no money.