If you are hearing a hissing noise it could be your carbonation canister is loose. To fix this problem, ensure that the carbonation canister is secure. Please be aware that recent carbonation bottles have been recalled due to bursting under pressure.
Hey Hailey, to avoid the soda from leaking all over the counter, double-check that the carbonation bottle is in the correct position. You simply need to insert the bottle at an angle and push the bottle towards the device to secure it. If you are hearing a hissing noise coming from your SodaStream Source, the carbonation tube is leaking gas, or the carbonation bottle is leaking, use the SodaStream Source is Leaking Gas problem page to fix the leak. If your SodaStream Source is leaking during carbonation, see the SodaStream Source is Leaking During Carbonation problem page instead.