The CustomVolume Mod allows you to set custom volume levels for each sound in Minecraft.
How to use:
Install the Mod as usual (this is not a Forge mod!).
If you have problems with Minecraft v1.6 or later have a look at this video
The config file is located in "mods/customvolume" (relative to your .minecraft directory).
You can assign relative volume levels to each sound in there.
A full list of all standard sound names is available here.
Due to the tree structure of the sound names, it is possible to assign values to superior "nodes" as well (eg. mob or mob.zombie).
These two lines basically cover most possible situation.
The first line lowers the rain noise to 20%.
The third line doubles the loudness of all note blocks except for hat and pling.
The second and fourth line overwrites the value 2 (assigned in line 3) with 1 and 1.5 respectively. As you can see, the line order doesn't matter.
This mod (plugin, a patch to Minecraft source, henceforth "Mod" or "The Mod"), is property of the Mod author (bannedtom aka tomix1024, henceforth "Owner" or "The Owner").
The Mod is provided 'as is' with no warranties, implied or otherwise. The Owner of this Mod takes no responsibility for any damages included from the use of it. Use of this Mod to be installed, manually or automatically, is given to the User without restriction.
By default it may only be distributed on http://www.minecraftforum.net. It may only be mirrored or reposted with advance written permission of the Owner. Electronic Mail is fine if you wait for a response. URL shorteners or other attempts to make money off The Owner's Mod are strictly forbidden.
* Fixed a fatal bug (If 0.1.0 didn't work for you, try this version).
If you have any questions, suggestions or anything else, feel free to post it here or write me a pn.
If you like this mod, you might also like my other mods ChatSounds, WebChat and SapplingSpawn.