I recently purchased a 98 Legacy GT with 113k on it. After driving it just 300 miles it has developed a knocking noise. I checked the oil level and it is fine and the knock will go away at idle but will come back after I accelerate. I realize that a new engine might be in the near future. I wanted to get some imput on how to tell the difference between piston slap and a rod Knock. I am about to put some thicker weight oil and a bottle of lucus in and just run her till she dies. Any sugestions would be great!