Knock at idle? Its definitely not detonation... My guess is rod knock. I had it on my engine from running it too hard (WOT high speed runs for several minutes) and that's why I had to do a swap. If you crack a the block open soon enough you should be able to replace the rod bearings for $100. I would recommend getting the ones COBB makes; they are supposed to be a better design. If you run it hard or run it too long with rod knock you are going to score the crank, and then chances are it'll be cheaper/easier to replace the whole block. Here is what rod knock sounded like on my engine; http://www.powerlabs.org/movies/engine.MPG Easy way to tell; pull the spark plug wire from the cylinder that is knocking; does the sound go away?
Holy cow that's aweful, i don't think i've ever heard knock that loud or clearly before it soundsd like your rapping on the intake with a wrench or something
ummm, just so everyone doesn't jump on teh "rod knock" train... Most subaru's have some piston slap because the engines are aluminum and space is needed for expansion when they get hot.
...And don't rule out the timing belt tensioners that even some "master techs" at aftermarket shops don't figure out.
