Well I replaced a 2000 2.5 SOHC in my Forester with the same engine except it's a 2004. Everything went well, it runs fine but there is a noise I don't remember hearing before. It is kind of a low humming sound, it is NOT rpm or even engine related because I can get the sound briefly with the engine off. After turning the key to on position it happens for a few seconds then stops. While the engine is running it is continuous, same pitch, same volume.
Does the fuel pump sound like a possibility?
I can't see how a swap would cause any change in the fuel delivery system, maybe it was always there and I'm listening more closely now... Any ideas? Thanks