It could be many things. You would have to investigate more closely to determine where that noise is coming from. It sounds like something in the valve train has broken but closer examination is the only way you're going to find out what it is.
January, 19, 2011 AT 3:40 PM
Remove valve covers/plugs and rotate engine by hand, watch the rockers closely for equal movement. Also consider a bad cam lobe especially if you hear a popping sound.
January, 19, 2011 AT 4:57 PM
If it isn't the upper end (head/valve train), then it's the lower end (sorry) & you might have a bad piston (broken ring or loose wrist pin). Start motor & with screwdriver in hand (put screwdriver up against head or motor block & listen for noise) start searching for approx. Location of rattle noise. This test should point you in the direction of which area the rattle is coming from.
Ford Man in Michigan
January, 19, 2011 AT 5:18 PM
If you do both a wet compression test along with a dry test, you should be able to distinguish between upper and lower end.
January, 19, 2011 AT 6:14 PM
Wrenchtech.I admire your knowledge, experience, & education while answering questions here at 2car! While i'm not a certified or ASE tech, I have been turning wrenches since the mid-1960's & have tons of experience to back up my ideas! I'm here to try & help others determine the answers to their automotive questions, and NOT compete with guys like you who KNOW lots more about the modern day autos ! Again. Thank You for your answers.I'm learning !