What could be causing battery drainage? 2006 galant 39,000 miles. new replaced batt. out in 2 months. pls hlp!

Scenario: I have a 2006 Mitsubishi Galant ES. I bought the car with about 25,000 miles on it in Dec. '06. It now has 39,000 miles on it. The initial battery went out about 2-3 months ago so I bought a new one. When the new one was placed in my car, it worked fine. However, this week (only about 2 months after installation) its beginning to need jumps all over again. If anyone knows anything about the newer model Galants, the lights go out afterwhile if you leave them on, so that's not the problem. I've considered it being the alternator or starter. Also, there is like a big metal to metal noise under the hood as well. It only really sounds off when I'm pulling off, when I'm on a constant go its silenced. Someone suggested this may be the engine. What do you all think? PLEASE HELP!