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..
Brand new last season. I have 2 of them so I can clean one at leisure and maintain filtration of the pool.
I know I can run up to 1500 ish RPM without inducing the noise.
Running lower speeds is certainly an option. With the robot I don't really ever need to vacuum . I've been trying to stick around 1500 RPMs because that seems to give me half decent flow into my skimmers while at the same time only using around 250 watts.
Maybe I should attempt a more thorough cleaning of my cartridges with perhaps a commercial filter cleaner?
So, riddle me this: I took the cartridge out to test and see if that made a difference at the end of June.... Life got in the way and the pool has been running filterless since then, just getting cleaned by the fine mesh filter in my robot....
Over the weekend I was in the pool with goggles and noticed a bunch of "stuff" suspended in the water, and decided that I needed to finally get the filter back in and just deal with the noise until I replace my filter. Put it all back together and...... silent.
I don't know if maybe the cartridge wasn't seated right or something????? WHatever it was its gone now