Presume you have the common, 3 blade, single belt, rider 40" belly mower & greasing the spindles, drive shaft & U-joints didn't help? Besides "bearings and belts" there's an idler pulley & pivoting tension arm that might need attention. These can often be nursed along by oiling.
A supplier like Richard's L&G doesn't need much "ID" to set you up w/the replacement parts to rebuild these decks. Just describe your 40" deck, they'll know which parts.
However, if it were mine, I'd try to isolate where the "unique noises" are emanating from 1st. If a U-joint is going, replacing the deck's "bearings and belts" ain't the fix. I've had drive shaft UJs w/and w/o zerk fittings. I'd disconnect the shaft & feel the UJs & remove the belt & feel each spindle. If I found 1 that wasn't glassy smooth I'd just rebuild what's bad. Deck gearbox issues can also produce "unique noises". Again, feel for trouble when belt is off.