I've been printing B&W for the best part of a decade and have never had a problem with Newton's rings. I assumed I had anti-Newton glass in my neg carrier. I've just started colour printing and I'm getting loads of rings from a roll of Ektar.
So, are colour negs more prone to Newton's Rings?
Flat bed scan then digi P&S: there's at least 5 rings on this print.
Apologies for the colour balance, it's a test print that the digi systems have taken to 'correct' (wrongly).