Originally Posted by GurthBrooks
Thanks to everyone who gave their input. I was told that the reason for the vibration and sound is from installing (Ford Racing gears) two separate shops told me this. I was told they are known to be very noisy and have a vibration. Both sets that I have used were Ford Racing 4:10 and now 3:73. Im having a hard time believing that Ford Racing gears could be the reason. Has anyone ever heard of this?
No it's not the ford racing gears causing this. There is an off brand of aftermarket gears that DO have that issue though - Motive gears. The Ford gears are the best ones you can buy for an upgrade on a Ford.
What caused you to replace the Driveshaft two years ago? What did you replace it with OEM or aftermarket? I'd look at the driveshaft first. Take it to a driveline shop, preferably one that builds driveshaft. They'll have the proper equipment to check the trueness and balance of your existing driveshaft and U-joints.