Ok I apologize ahead of time if this is in the wrong place, and also I am not very good with mechanical details. But here is my problem. My Subaru Forester has 160k miles, and today when I went to start it, it make a horrible knocking/tapping noise coming from the engine, and this is just sitting idle. I had someone look at it and they think it might be the rocker arm?, or a problem with the intake or exhaust valve. Im curious if this sounds right, or if anyone has had a problem like this. My father in law is a mechanic and said I could use his tools etc but Im curious how big of a job Im looking at and would I run in to any other problems tearing the engine apart. Thanks ahead of time. I hope I explained everything ok.