OP, unfortunately I think this is pretty much an inherent flaw with many MR frames.
I've dealt with this issue with my MR frame for a number of years now. Really too bad because I love the fit/funcrionality of my pack. (use MR GLMT frame with mule bag for day hunts, selway bag for longer trips). I know a guy with a pintler, same thing.
Makes no difference to the squeak which bag is on the frame. Like someone said above, really cinching down the load lifters helps but then you are sacrificing your preferred comfort/fit to stop an annoying squeak.
When I'm looking to replace my pack, the squeak will be the reason I will try another manufacturer.