I'v been running a Purolator Pure One filter for 3000 miles now, and this week started getting a knock on startup in the morning. I checked my oil and it was down about 1/3rd a quart from full. I topped off the oil and the knock is gone.

I know sometimes the filters get blamed for having bad anti flowback valves, but at least with my Jeep, a full oil pan fixes the issue.

 

i'll have to look into that