NoteBetter is a simple Forge coremod which adds a JSON for configuring note blocks. It allows you to assign a specific sound (any sound you want!) to a specific block or material, all from a config file.
For example, you can set enchanting tables to play the xp orb pickup sound, anvils to play the anvil landing sound, pistons to play the piston sound, and iron blocks to use the unused "pling" sound.
NoteBetter can be seamlessly installed in any Forge server. Your players don't need it installed on the client in order to connect. (They might need a resource pack, though.)
NoteBetter is fully backwards compatible with most Forge mods. For example, Thaumcraft Arcane Ears will pick-up all vanilla/default sounds.
The format specification is available on github.