[tundra39]

Thought I would put in my 2 cents worth. I was a field tech for Wix filters awhile back.Fram was the worst spin on oil filter on the market.Yes it has cardboard end caps, a very weak anti drain back valve & very irregular spaced paper pleats.It's filtering factor was rated a 33 micron, which is the size of a hair on your arm. However there was no SAE measurment for microns; so their 33 micron could have been what ever size they put in their pleated paper.The start up engine knock you are refering to is caused by the weak anti drain back valve, not holding the oil in the can, like someone stated.Also some filters have a by-pass valve in the filter if required by the vehicle manufacture. It was also weak.When it malfunctions oil pressure gets too high & blows the filter off the mount.
Purolator was also not a top grade filter. It had a piece of common string wrapped around the pleated paper & very irregular pleats in the paper like fram.What do you think hot oil does to the string? They did have metal end caps& a good anti drain back valve.

Wix & napa gold are excellent filters, in oil,air
& fuel.Air & fuel are a whole
issue by themselves!
Just wanted to pass along my experiences in the field.

Tundra 39