Just last week I started getting this loud vibration at 3500 rpm under load. It is this just for a split second then once i get around 3800 rpm it goes away. It sounds and feels like it is coming from the tranny. I have 50K on the car with the stock clutch and some minor mods.

Has anyone had this similar experience?

 

I have been trying to figure out a similiar vibration\rattling which seems to be drivetrain related. On deceleration and about 2k-3k I have this consistent rattling that is similiar to IC pipes rattling . Of course I've done a preliminary check but nothing. I'm planning on diving deeper into it when I have a chance.
Let me know if you find anything.