My 2002 WRX is completely stock, and is now making a knocking noise after a bad coil pack caused misfiring? The rods don't seem to be bad I had the oil pan off and removed spark plugs while the car was on making no noticeable change. There are no shavings in the oil, also there is no smoke. The belt tension-er seems to be fine. It's definitively not piston slap. When you give the car a little throttle around 1k RPM the sound is near gone. Compression is completely fine reading 150. Also, the car has all the horse power with no decrease. Sea foam stopped the noise for about 35 seconds when it was half way warmed up, but then it continued to knock. Does anyone think it could be a hydrolysis follower not building up pressure and slamming shut? Any help will help.