Oil/Knocking

[Duke123]

Ive been having problems recently with my 03 Murano (100k). I started hearing some rattling, which seemed to be low oil initially. Even after the oil was topped off, there was still a little rattling when accelerating. Now I'm only 1500 after my last oil change and I'm down a quart of oil. There doesn't seem to be a leak (or at least nothing on my driveway). This started a few oil changes ago, and seems to be getting worse. The mechanic scratched his head, couldn't find a problem and gave me an additive which he said would fix the problem in a few oil changes. I'm not really buying it. Any thoughts?

[Macsleuth]

Hmm, might have someone start it while you are standing behind it to see if any blue smoke comes out of the exhaust. knocking noise could be carbon build-up, in which case, cleaning the carbon off the rings might fix the issue. Good luck.