Weird Engine Sound...

Well, I am not an expert on sounds...but i'm getting a slight fluttering from my engine....started yesterday....haven't changed anything to cause this......what am i looking for? Maybe she needs an oil change? There is no leakage of oil.....and I've only had to add one quart since I bought it 3 months ago. Car has 162k miles on it, and I only use 91 or 93 gas in my car.....I'm at a loss....it sounds like it is coming from one place...but when I put my head under the hood.....it's hard to locate the sound....i put my head on the passenger side...and it sounds like it's coming from the drivers side.....and I put my head on the drivers side...and it sounds like it's coming from the passenger side....it's weird.....could it be a lifter tick? or knocking? i'm not sure what either of those sound like.....if it's internal.....what do i need to do