I have a 2004 F-150 with the 5.4 ltr and auto transmission. Several years ago I began to experience starter grinding on the flex plate. I then noticed two distinct clunks from the drivetrain when starting out from a stop. I figured it was u-joints but didn't change them because mine are the staked in type, (a whole different problem). Anyways the grinding got so bad that I had to do something about it. I took it to a mechanic and he replaced the flex plate and starter. There was about a 5 inch section where the teeth were completely ground away on the flex plate. I got it back and it started just fine. Leaving I noticed that the clunks were gone and it was as smooth as the day I bought it. My mechanic told me the u-joints were fine. I have been enjoying the smooth start and lack of grinding for about six month. The other day I went to start it and the grinding returned. At the same time the clunking, (although not as bad) came back. It is almost like something shifted and is causing these problems. Please any help with this. Has anybody heard of these problems? Thanks for your help.