Not much to go on- but my first thought would be-
-Vibration(s), many causes here, a couple would be Bad U joints, unbalanced driveshaft, bad pinion bearing..
Is the car lowered ?
If it's lowered could it be jamming the driveshaft into the trans.
Is it the original driveshaft to the car?
Is the trans mount in good shape?
Does the car make a bunch of power?
Wish I could be more help,hopefully some of my suggestions might help you. Hang tight and smarter people will pop in with things to check etc. lol
I think @RaggedGT hit most everything I could think of off hand. Bad output bearing maybe allowing excessive runout leading to stress cracks. Maybe pinion angle binding the u joints.
The car is basically stock not lowered pretty sure it is original driveshaft only upgrade so far is a cold air intake so not a ton of power just replaced trans mount
I would try putting the car up on jack stands (all 4 wheels off the ground) and let the car idle in gear. Watch for a wobbling/bouncing driveshaft or whatever is vibrating
Ok will do I got a new tail shaft housing for it an I'm going to put that on this weekend don't currently have the car it's 80miles away at my dads house
The stock driveshafts in these cars were trash. Very bad about vibration. The only known cure is the aluminum ford racing shaft. (Common fix) I put one in my car and it was smooth as butter afterwards. That vibration will tear upall sorts of stuff.