There's no sound in-game at all, and the console is spammed with all errors of the sounds not being found

 

Example:

Unable to play unknown soundEvent: minecraft:step.grass

 

I've actually never touched the sound file yet, unless something went wrong with the installation.

 

Could anyone help me out?

Is this with 1.7.2 or with 1.7.10 (note the latest forge versions are 1.7.10)?  For 1.7.10 you need to add some more arguments to the run configuration "--userProperties={} --assetIndex 1.7.10 --assetsDir C:/Users/Aaron/.gradle/caches/minecraft/assets" otherwise you'll get a sound error like what you're describing.

For 1.7.10 you need to add some more arguments to the run configuration "--userProperties={} --assetIndex 1.7.10 --assetsDir C:/Users/Aaron/.gradle/caches/minecraft/assets"

...Translating "C:/Users/Aaron" into whatever your filesystem uses. I am trying this now...

 

UPDATE: I got sound, but I needed to do a couple things differently on my ancient WinXP machine. Firstly, the .gradle file hierarchy had assets, but /virtual/legacy was empty. Since I saw my primary .minecraft app data nearby, I found the path to its assets instead.

 

Secondly, XP uses the old C:\Documents and Settings\...  structure, and the spaces in the path string require quotes to pass as an argument.

 

Putting the two moves together, I got this argument for my run configuration, and miracle of miracles, it works:

 

  --assetsDir "C:\Documents and Settings\Jeff Fisher\Application Data\.minecraft\assets"