Jim,
It this were my pool, I would just run the pump at a speed where it makes no noise... and not buy a new filter, at least for now.. 90% of the time I run my pool at 1200 RPM and it works great. You know you can set the speeds to what you want, you don't have to use the default RPM..
I know you have decided it is a filter problem, and it may be... But, there are a ton of other people who have that same pump with relatively small filters and they do not seem to have an issue.
I can't help but wonder if the fact that you have an APG has anything to do with it?? (Grasping at straws here..) Normally the suction side is.. well, sucking... But with an APG you would think it would be under pressure from the water in the pool.. Not sure that would be an issue or not but if this were my pool something I would be looking at..
Is the cartridge in your original filter old?
Thanks,
Jim R.