I just raplace my NGK/BMW spark plugs with new BOSCH SUPER plugs on my 95' 540i. While I had everything apart I replaced my valve cover gaskets as well. Just put it all back together tonight and now I'm hearing a rattle or a light knocking noise coming from the engine as soon as it is started. It's almost like the intensity of the noise will get greater then lessen and the pattern repeats itself as the motor is running. The noise doesn't go away. Any ideas on what this could be? Thanks in advance.