I am prepping an old kitchen for a new floor and cabinets. The carrier beam is about 5/8" high on the kitchen end of the house, but is level at the other end. This leaves a "hump" in the kitchen floor that is from 3/8" to 5/8" high, about 34-36" wide and runs across the ~10 ft width of the kitchen.

The rest of the kitchen floor is nice and level.

The current floor is 1979 vinyl. It's coming out. There is a 5/8" plywood underlayment, and then a 3/4" plywood subfloor.

Bringing the rest of the kitchen floor up to the hump level is not an option -- the floorplan is open and the new floor will join existing hardwood evenly.

Am currently considering two options:

1) using a power planer to reduce the hump to a less-noticeable 1/8" to 1/4" by shaving off much of the underlayment across the hump. This would leave a 3 ft by 10 ft area with a very thin underlayment, but thick enough to hold screws so it's stable.

2) using the power planer to eliminate the hump entirely. This would create a 'feather edge' out of the 5/8" plywood underlayment across each side of the hump that would be about 16" wide (about 2" across the peak of the hump would be taken down to the subfloor). I could probably pull up the feather edges a bit, get some adhesive under them, and screw the parts that are 1/8" and thicker. I don't want these edges to squeak.

Any thoughts on this approach, or better alternatives?

Thanks.