battery 'sizzling' noise
sounds like the acid is bubbling creating H2.  Could be dangerous cause it's combustible if it's venting under the hood and there's an open spark.  That's one reason why they have you jump a battery in particular order so you don't spark the terminal and ignite any fumes under the hood.

Did you charge it recently? maybe too fast or over charged? 
I'd take it to autozone and have them do a discharge test.  It might be weak under load which would point to failing battery.