Raise the deck as high as you can .
Put your hand under the deck and find the blade
If the blade goes up & down then one or both of the spindle bearings has collapsed
Usually the right one goes first as the right blade has to shift all of the clippings out the chute + do it's own cutting.
If you paid the extra for a flip up deck model, now you will find out just how much it is really worth.
Flip the deck
If not
Put some 2x4's under the deck, left right to act as rails
Drop the deck on the 2 x 4's unhitch it then slide it out to the right IT IS HEAVY
Flip the deck and check that all of the blade will spin freely & quietly.
They can have a very small amount of up down play but the blade can not rock left right or see saw
Spin all of the other pulleys, they should also spin quietly & smoothly .
Replace any pulleys that are noisy, rough or rock
Spindle bearings get replaced in situ they are all standard bearings , but get them from a real bearing shop not ebay or amazon so you will be guaranteed to get good bearings
THERE IS A BIG DIFFERENCE BETWEEN $ 5.00 BEARINGS & $ 20.00 but paying $ 20 on Amazon will just cost you more for a $ 5.00 bearing.
Branding on the rubber seal or the box means nothing as bearings are the most counterfitted product on the planet .