I have a Pontiac Bonneville with a 3800 with 144,000 miles. I fueled up at a filling station ad when I started the engine I heard it knocking. Sounded like it was coming from the top side of the engine but the I noticed that the oil pressure gauge was fluctuating bad. Car is in excellent shape and motor uses about 1/2 qt on a 3000 mile oil change interval. Where do I begin?

Our oil gages are notoriously unreliable, and most times I tell people to ignore them. In this case, however, when the reading fluctuations are accompanied by engine knock, I suggest you not drive the car until you figure this out. I would start by getting a proper oil pressure gage and using it to see what the actual oil pressure is. You may also want to invest in a mechanics stethoscope ($10) to help narrow down where the knock is coming from.

Check your oil level and coolant level also. Me thinks you may have eaten some lower end bearings.

Being a 2000, do you know the complete repair history of your car?

To Mike'* point, you might want to drop the oil pan and see if there are any pieces of metal in there.