Loud injectors are a common/normal Toyota idiosyncracy, they may get louder with age, but I don't think a stuck one would be the cause of them getting louder. With the age of the truck, it would be a good idea to pull all of the injectors and have them cleaned and rebuilt. You should be able to find a shop there in Fremon or San Jose that can do it. The place I use in Sacramento charges $32/injector to clean/rebuild/balance.

If you pull them yourself, be caerful not to disturb the knock sensor wire, it gets brittle due to the heat and will break on you. You might also want to replace(relocate) the PCV valve as well. If you have a shop do the work, you should have them adjusted(shimmed) valves since the upper intake has to be removed to do the valves.