[fiveohpatrol]

Another vote on the oilpump driveshaft.

I have a feeling you will end up having to remove the engine, and then after you pull off the oilpan, you will find a few pieces of what looks to be a steel "Twizzler" and the oilpump locked up.
Upon further inspection, the bearings will be scored, and needing replacement.

This happened to me a couple years back.

Also, if you decide to cut the filter open to check for particles, you will have to cut it open with a large tubing cutter, or some other cutting tool that won't get metal shavings into the filter while you are cutting it.
I would think that cutting an oil filter open with a hacksaw or similar device would introduce more metal shavings into it, and you wouldn't be able to tell which ones were from just cutting it open, and which ones were there before. Am I thinking right Jeff?