My mechanic (former Nissan tech who went independant) told me that my '97 SE gave a knock sensor code in the computer. It wasn't a "hard code" which makes the check engine light come on but may start giving me problems. I can sometimes hear a knocking sound under hard acceleration coming from what seems to be the right side of the engine bay. It's not there consistantly but it is frequent. Could this be the knock sensor? Has anyone replaced theirs before a check engine light appears? Did it make a noticeable difference? I've heard Courtesy Nissan has them for $120 shipped. Is there a contact there to talk to as their web site has it priced higher? Thanks.