Here's the deal. Yesterday I did a tune up on my 91 5.0 GT. This tune up happen to consist of a oil change. No big thing there. So I drive the car around a lil bit that night...no problems. It was raining too so I really didn't beat on it much. Now this morning I fire it up and the first thing I hear is this nasty ass metallic knocking noise. I almost $hit myself at that point. I decided to tempt fate a lil bit and let run seeing if it would go away as the motor warmed up. Nothing. So I figured it was lifter that might have been bad and needed the time to sit over night to drain out and screw up. Needless to say now I have my mustangs top end apart in my garage (heads are still on) and the lifters are fine. SO if anyone has any suggestions or input on this that'd be great.