How many hours on yours ? My TC 4260 has 84 hours & quiet, @ 3.5 yrs old.
But you could easily remove the deck, & check each spindle & each pulley by hand rotating each separately for noise & or excessive looseness.
The decks come off very simply & doing so un-hooks the deck belt. It's described in the owners manual or Youtube.
Deck removal: Lower deck to lowest setting, remove front connection point at deck. Let it on the ground, gently push deck back towards rear of machine so the 2 rear lift hooks unhook off the lift bar, the deck belt will loosen (Pay attention to where the belt goes for re-assembly) & remove it from machine.
Then check each (one at a time) by spinning each by hand & listening. The guilty party should be revealed. Replacing either a spindle or a pulley will be pretty much common sense then.
Good luck & Keep us posted to what you find.
Put two lengths of 2 x 4 , flat side down under the deck about 6' to 8' long.
Drop the deck to the lowest setting and proceed as above.
The deck will then slide out on the 2 x 4's very easily.
Check the blade by grabbing them on the ends then try to rock them see saw motion.
Any movement = new spindle bearings.
Check all of the other idler pulleys on the deck as well.
Any noise or roughness = new pulleys as the bearings are not readily replaceable and most are double row so not readily available.
To remove the drive pulleys & Blades an impact gun is your best friend.
Take the pulley nut off first because you can hold the shaft with the blade.
then the blade nut off again holding the blade.