The rear most shaft on my driveshaft slaps the bottom of my car under heavy boost or load. I replaced u joints and carrier bearings to no avail. Just started doing this after I put new transmission and clutch in car. The transmission facing m8 bolt on the transmission with dowel pin is stripped could that cause this? Or could it be a bent drive shaft or something else?

Could also be something like a carrier bearing or out of balance like it is bent. See if that stripped bolt has been hitting anything

Thanks for the reply. Going to bring it to driveshaft shop and have em check it out.