Maybe the Napa filter is a finer micron filter than the Bota filter and causing some cavitation problems when cold?
This would be my guess if I had to guess, but in my interest of wanting to learn and know, I dont like guessing.
The noise in the pump sounded like if gears were hitting dry, or if a bearing was going out and was spinning at high revolutions. Hard to explain. But it must have been the filter as I say, no noise with the kubota filters back on.
Seems like others would have had this issue and reported it to napa. My local store is sending the hyd filtr in for testing and I will know those results near end of decembr, but since 2 different napa filters (same filter number) made the pump make noise, I am feeling napa wont find that it was a bad filter, so I will still be left with questions. I guess I will see.
I will chime back in when I get those results from napa.