I'm sure this was working in the past, but in the latest versions, I've not been able to hear anything through portals, even a note block hooked up to a redstone clock.

Tested with only BP 0.3.7.7 and Forgelin 1.8.4, with both the Latest and Recommended versions of Forge (14.23.5.2768 and 14.23.5.2847 respectively).

EDIT:
In the same vein, I'm not seeing any particles get generated on the other side of the portal. Weird.

After some more testing, I discovered a tucked away Clothesline Hooks .jar file.
After deleting that, I'm able to hear sounds and see particles from the Overworld while in the Nether, but not the other way around.
So, sounds will be heard and particles particles seen from Overworld>Nether, but not Nether>Overworld.
This doesn't change with reloading, either.
EDIT:
I've just restored the Clothesline Hooks thing, and I'm still able to hear from Overworld>Nether, but not the other way around.
Perhaps it's always been the problem? I do recall mostly testing from Nether>Overworld.

I've re-enabled every mod I was using, and I'm still able to hear sounds Overworld>Nether, but not the other way around.
Interestingly, particles stopped generating on the opposite side again, regardless of which I'm on, as opposed to just not generating Nether>Overworld.

Looks like it's Random Patches breaking the Overworld>Nether particles.
Still just something with Better Portals breaking Nether>Overworld sounds and particles, though.
EDIT: Specifically, it's the 'particleFixes' option breaking the Overworld>Nether particles.