hi, so I have a 2003 legacy L and had done the headgaskets three times in the last year and finally decided something else needed to happen. I took it to a mechanic and he rebuilt my engine(2.5L) with a 2.2L block, he said that the heads were warped and he machined them down 5/1000. I have just got the car back and it seems to have a knocking noise coming from the top of the engine, also after a quick test drive a noticeable lag/loss of power. Any Ideas? was this bad or good?