The restrictors are there to limit flow velocity. Basically non adjustable flow controls to make the deck move smoothly at a reasonable speed. Either they can move in the new cylinder or there is air in the system. Noise in hydraulics is almost always from air bubbles. How much have you run it since changing it out? A small cylinder with long hoses will often not move enough fluid to do more than move the same fluid back and forth in the hose. The only way to really bleed them is to open fittings under pressure. That tends to get messy.
If the deck is moving really fast, maybe smaller restrictors are called for? I wouldn't expect the orifice size to have any effect on the noise though. With everything working as it should I would expect no fluid flow with the deck lifted. Since you are getting noise, maybe there is fluid running thought it all the time keeping the deck lifted? If that's the case, the noise could be from fluid moving through the valve that should be keeping the fluid from moving. Basically the valve could be chattering from trying to maintain the pressure needed to keep the deck lifted.
