Basically, you need to go through the saw. Just because bearings are sealed, doesn't mean they don't go bad, only that you can't grease them. They usually last a long time and I wouldn't suspect them as the cause. Very often, it's a drive belt or pulley that is loose. The Unisaw should have three drive belts. Before doing anything, unplug the saw. Remove the blade. Check that it was free to fit against the arbor collar. You know that you only tighten blades finger tight, you don't use a wrench or you can bend the blade. The blade can get caught in the threads of the arbor or there can be some debris on the collar, either one, inner or outer. It may just be tension on the belt/s. Also check the alignment from pulley to pulley with a straight edge. A bolt or two may have loosened, allowing the motor to shift, releasing tension and going out of alignment. There is an allen head set screw in the grooves of the pulleys that often align with a key, a small rectangular piece of steel or a flat in the shaft. These can come loose. If the belts are off, you can turn the arbor by hand, like trying to break into a safe, to feel any roughness in the arbor bearings.
This is always a good time to go completely through the saw, checking every bolt. Don't over tighten any since tapped holes can easily strip. Open the electrical switch, clean all the dust out, under the saw, lube the lifting and tilt mechanisms, check blade alignment, set the fence, miter bar, reset the angle indicators, etc. Every saw should be gone through from time to time.
Well, I may as well get this party started. The finger tight thing is, in general, probably not one of the better recommendations for Joe Public. It is also not the blade changing procedure by any saw manufacturer that I can find. Just a few offerings:
From Delta's operators manual:
CHANGING THE SAW BLADE
USE ONLY 10" DIAMETER BLADES WITH
5/8" ARBOR HOLES, RATED AT 3450
RPM OR HIGHER.
DISCONNECT MACHINE FROM POWER
1. NOTE: Two 7/8" wrenches are supplied with the
saw for changing the saw blade: a box end wrench (A)
Fig. 69, and open end wrench (B).
2. Remove table insert (C) Fig. 69, and raise saw blade
to its maximum height.
3. Place the open end wrench (B) Fig. 70, on the flats
of the saw arbor to keep the arbor from turning, and
using wrench (A), turn the arbor nut toward the front of
the saw. Remove arbor nut, blade flange, and saw
4. Assemble the new blade, making certain the teeth
point down at the front of the saw table, and assemble
outside blade flange and arbor nut. With wrench (B) Fig.
70, on the flats of the arbor to keep it from turning,
tighten arbor nut by turning wrench (A)
5. Replace table insert.
(All other manuals are similar)
I am not advocating that you do anything differently than you do. But the overwhelming consensus is to finger tighten, and then add 1/4 turn on the nut. Snug but not tight.