Check the inside of the saddles too, if they have any grooves or wear new inserts probably won't help much. I encountered the same problem on a Jackson branded FR years ago, the saddles were garbage.
I believe you can ID the earlier 5881s by their "stapled" plates. The later Sovteks have welded plates if I'm not mistaken. I think the print is slightly different too but I don't have any of the later ones on hand at the moment to confirm.
Simple, it's not in tune. When you attempt to tune your E and D strings to standard pitch the A will go flat. The string tension has to be balanced with the springs. Anytime you change pitch on a string it will impact the others.
I have an '02, it has a little mechanical hum from the transformers, it's always been that way. I suspect it's more noticeable when you have an open headshell like Soldanos, as opposed to a shell that has far less venting.
All the handwringing over FRs. Once you spend some time with one they're really not that difficult. The tuning stability far outweighs the little extra effort during set up.
I typically like heavier music but I co-founded this band in '97 and it evolved into a successful 20 year run, and much more fun than I would've ever imagined. This one definitely made the most $$$ but I've suffered some abuse for the material.😆