Knocking During Cold Start-up

Some years ago I had the same problem with a 6 cylinder Ford van. I used a cheapo oil filter from KMart (Motorvator, IIRC). Either the drain back valve was bad or it was non-existent. Switching oil filters solved that problem. I don't know anything about the Pure-One filters but you might try one from Toyota parts. That will at least give you a frame of reference. That would seem to me to be the easiest and cheapest first step.

There are few reasons for the condition you described: Some wear on the cam bearings (could be caused by long time use of low quality oil and filter) Leaking exhaust manifold gasket Loose or cracked exhaust manifold heat shield I would recommend to remove the valve cover and check for dark brown hard deposits under it. The engine flash in such case would just lift this crud and carry it into the oil pump passages. I would recommend to use OEM oil filter, and Valvoline 20W50 oil in summer. In addition, the noise can be produced by timing belt idler bearings or (real case with my customer) by alternator front bearing.

It could be crap oil filters without functioning anti drain valves, try a Toy filter. I would not flush it but rather pull the valve cover and hand clean it.. But mine is noisy to sometimes.

Since the knocking continues after the oil pressure comes up, it's not going to be valve clatter. One possibility is piston slap. My '83 developed that at about 200K miles. I get a rattling, almost diesel sound for about a minute on a cold day. Car has 250K now. All I've done is to drive slowly (or just let it idle) until the noise goes away.