Up until now I've been doing my 8x10 contact prints with just a hinged piece of glass. No problems.

Now I have a new contact printing frame (photographer's formulary) with clean glass and I'm getting newton rings on one particular area of the neg I'm printing today. I cleaned the glass and repositioned the neg but they appear in every print (in the same vicinity) about the size of a dime. That area of the print* is bright white tone I can't see residue or defects on the neg. How do I fix this?

*kentmere glossy fiber