Regarding the "knock", I've had a similar experience as many of you. Mine is an '03, HO.
My experience with the dealer has been the same as many of you, also. "Can't fix what you can't see or hear".
I just got back from May Madness where I ran into a gentleman who mentioned that the dealers have a "recording device" that connects to the OBD port (I believe that's what they call it) under the dash. You plug it in and when the engine starts knocking, you turn on the recorder and capture what's going on with the engine. This device is designed to help with problems that happen everywhere but, at the dealership. This has been my problem. The knock is quite intermittent and never at the dealership.
I don't know if this is the answer to the diagnosis problem but, I thought i'd share it with you anyway.
Joe F. (Buffalo)