Windows .exe Huge bandwith consumption by java when joining a server

[Grobzoula]

Hello there.
I have a really huge problem for a week now, and I tried hard to solve it, but I didn't succed.

When I try to join a server, java starts to download something and consumes my entire bandwith, causing a lot of latency. In game, I have to wait almost 30 secondes before being able to do something. If I try to move and go into another chunk, it starts "downloading". What does it try to download, I have no fucking idea.
According to Netlimiter, the DL Speed reaches 64 000 when I join. It gets lower if I don't move, reaching 30 000. If I try to move, it goes up again.
I do not have this problem when playing in singleplayer mode.

Here's the console log when I try to join the server.
http://pastebin.com/bEZ3pbSm

I tried once to put a DL limit for Java with Netlimiter. It makes me lag even more in game, then crash the game. Here's the console log when I do it :
http://pastebin.com/Aynshrne

I'm currently using Java 6u45 for Windows 7. Tried with Java 7 before. Already tried to turn off/on my firewall, my antivirus n shit. Already tried to reinstall java, Minecraft and Feed the Beast. Already asked the admin to remove my player.dat from the server.
None of these worked. I'm getting desesperate. Please, help me.

 

[Eyamaz]

First, you need to update to java 7 u21. Most mods are coded in 7.

second, be sure you uninstall all previous versions of java.

Finally, check to be sure you have the same versions of mods as the server, it looks like they've disabled at least secret rooms by your pastebin.

Sent from my HTC One X+ using Tapatalk 2

 

[Grobzoula]

Already did everything, didn't do anything.

 

[Eyamaz]

Not sure what to do with this one. Try porting it over to multimc and see if it still happens.

Edit: did you add any additional mods?

Sent from my HTC One X+ using Tapatalk 2

 

[Ashzification]

Try doing this: http://desk.feed-the-beast.com/index.php?/Knowledgebase/Article/View/9/0/basic-troubleshooting

 

[Grobzoula]

Not sure what to do with this one. Try porting it over to multimc and see if it still happens.

Oh wow, it looks like it worked ! It's not perfect, Java is still downloading things, but there is almost no lag now. I hope it wasn't just luck.
I didn't add any mods, I just use the standard Ultimate pack with the latest version.
Thanks for the help !