The length of connection to frame is still excellent - good job, Westwood Industries of Tupelo Mississippi!
I think to secure the edgewire the sinuous or no-sag springs are attached to, back to the frame just at the edge, will help end this squeaking. Each line of sinuous spring is secured to itself with strong little clips lined with thick paper, so you don't have steel-on-steel rubbing. There is chance the paper has worn away, producing a noise...that I can't go in and fix, but the edges for sure will help. Stay tuned to see the beautiful chenille damask that will cover this set, after a little repadding.