I wrote the below for a new thread before finding this bug already posted:
At around 20 blocks away from the windmills, they can't be heard, but sound processing can skyrocket. Placing many of them and walking just out of hearing range causes the sound processing (seen via MC debug) to rise fast. Walking back in range of hearing the windmills corrects the issue.
At 8 windmills and moving 20 blocks away, sound processing can go as high as 51% (not high enough to be a performance issue on my computer, but seriously high).
At 35 windmills and moving 20 blocks away, sound processing can go up to 73% and frames down to 2 fps.
At 16 geothermal generators and moving 20 blocks away, the same issue occures.
The sound of the windmills also continues to play once logged out of a single player world. Relogging within hearing range of these machines several times keeps adding new engine sounds on top of the original sound.
Standing next to the wind farm, logging out and then genning a new world causes the same 70%+ problem. Is the sound effect generated by machines not being disposed of correctly?
As I normally run with a lot of mods, I repeated the test with minimum mods:
CodeChickenCore-Client 0.4.1.zip
NEI
industrialcraft-2-client_1.64.jar