My spa has two pump. When the first one comes on all is good. When the second comes on, it works fine but it is much louder than the firts pump. It has a scream to it that does not sound good.

Is the motor going, or the pump?

The frame is a 56Y, so can I replace it with any 56Y with same voltage?
The current motor says "This is an unrated pump" I am assuming it is the HP that is unrated because is does not say the HP on the motor.

If I were to purchase a replacement, how big to I get?

It's a 1997 cal spas model A-4000, 6-person.

Your motor bearings are most likely the culprit.

Replace it with a similar amperage rating. Yours is probably in the 10-12 amp range.