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Well if your tank o-ring is looking alittle old or just beat up I would suggest replacing it. CO2 tanks tend to love to go through o-rings.

Now where is the coming from, the top of the valve or the side?? I'm sure if its creating a squeling sond is is most likely leaking some air. Your best bet would be to take it to a local shop or airsmith, if you take it to a local Paintball shop make sure they are experienced airsmiths and have a clue of what they are doing. If your going to mess with your tank yourself make sure all the air is out of it, wouldn't want you getting hurt.

Without being able to see and hear exactly what it is doing it is kinda trial and error style thing.

Hmmm... Still alittle puzzled by the problem. Are your threads on your tank damaged??? Your friend is most likely talking about Teflon tape though.

Well if the tank didn't do this when you first got it something must of went wrong but if the tank has been doing this sense day one I'd send it back to where you got it and say its a bad tank. Did you buy the tank from a big retail store such as Wal-Mart??? Their tanks tend to be faulty and don't last that long.

Like I said before it is hard to suggest what to do when I can't physically hear or see the problem.

probly need a new o-ring on the tank