Btw what is your fps? and are you doing anything in the background like rendering something or possibly have a lot of internet pages open especially youtube pages.
Well, if you've got 64bit installed and assign around 3gigs of ram to it and are still jittering the only thing I could think of is to try and install optifine but It's not really working right now with the pack, nei bugs and crashes.
I've been playing the pack for a bit now but I've been having an issue with not having any vannila sounds. I've tried copying and pasting the assests from vannila over to the packs assests file but nupe still not working. I've redownloaded and i've even tried to delete the weather mod but after that my mc just crashes on the mojang screen. Help?
I gave it a shot and it still is silent aside from the stupid weather mod makeing noise along with morph makeing the crunching sound when you change. As far as i can tell it's a bug when downloading. I'll keep working on it and let ya know if I fix it!
I've heard that mc will not load sounds sometiems if there's a lack of ram. But i'm having the same issue as you and it's obviously loading the audio beacuse you can still hear the wind. I'm kinda confused on this one.
Best chance is to ask for a refund or maybey have a person who's good with servers give you a hand. I'm sorry but i'm still working on getting my attack of the bteam to get up and having issues too.