Thunk when driving
 

I have a 99 3.0L manual and yesterday when i was driving I noticed somthing funny. It felt like a bump when i was driving but there was no bump. this also happend today a few times when i was driving. I will be driving at a constant speed and it will feel like it thumps. It doesnt do it all the time once or twice a drive. It feels like its dumping somthing on the drive train all at once but just for a split second. like I said almost like a bump.
can anyone help me.

This happens in all gears and at any speed i dont know what it is my guess is the rear end but i have no clue.
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possible u-joint going out...

Probably the slip yolk. You have to remove the boot that is on the driveshaft close to the diff and lube up the splines. Ford will do it but I'm not sure for how much.

I give up I have searched and tried to figure out what was wrong but I can't find it. I'm going to drive her till somthing breaks then fix it.