2003 Toyota Corolla rattling sound in engine

My car is rattling sound, thought running low with engine oil. I changed oil. But surprisingly oil is running low after between 700 and 1000 miles. This is something not normal. So I took my car to a near by mechanic and he told that let us try with PCV change. I did (charged 20 bucks), even after problem persisting. So please help me with your suggestions and views.

Thanks