I purchased my 2001 convertible in August 2001. Since new, it has had what seems to be a lower engine light knocking sound. It is most detectable at idle, which is about 600rpms for me (automatic). I am pretty sure it is not lifter noise, but rather perhaps ring or rod noise. With 4000 miles now, it is no better no worse. I am unaccustomed to such knocking with preious engines of any type. The Chevy dealers tell me stories that it is normal for the Corvette engine all the way to the Corvette engine uses solid lifters and it is normal. Does anyone have an answer to this?