Ok so I just put a new 3.8 in my 96 mustang and drove it for 4 days and decided to put new plugs in the next day it created a nasty knock the plugs the parts store gave me were about a quarter inch longer or so I'm upset about this since I bought a used motor that ran great converted my auto into a manual now I have to get another new motor any ideas on what could of happened to motor hasn't been abused since install rattle started in top end now its in the bottom thanks for any input