Forgot to report this. Almost all sounds are muted in rftools dimensions. So far I I can only confirm to hear the sound of collecting exp playing as usual. Even creeper explosions are completely silent.

This is the case for all dimensions I encountered so far.

What? That's extremely weird as I don't do anything in relation to sound. But anyway, I need to know what version of MC + rftools that you're using

rftools-1.9.0-4.46
MC 1.9; forge 1.9-12.16.1.1889

here is a full log of me walking around, killing a few mobs and opening chests.
http://pastebin.com/HrhtMSfA

I still get sounds from taking damage, collecting exp or landing on the ground, but all other sounds seem not to play. Sounds play fine in the overworld.

I cannot reproduce this. Must be some kind of weird mod interaction or something.

Thank you for taking the time to create this issue, as we're no longer supporting versions below 1.12, I'm going to go ahead and close it but if this bug seems to continue over to newer versions, please do report it again so we can investigate the issue further.