This morning I was coming in the gate (on base) and heard rattling coming from under the hood, sounded like a diesel, while idling it went away but under a little gas (between 1k and 1.5k rpm) it was noticable, and then wasn't there above 2k. Shut the car off and waited like an hour (until the sun came up) and cranked up and drove it around the block and the noise was gone.........maybe a stuck valve? Maybe a bottle of Lucas to help clean up in there?