Roar from underneath while driving...o on 1991 GMC Sonoma

I've replaced the manual transmission with a T5. I've put in Dextron/Equiv. fluid in this, as it is the recommended trans. fluid for it according to my Haynes repair manual... I replaced the rear seal in the transmission, awhile back and checked the fluid level in it, added a qt and a half into it. Any reason for this to continue to roar?

Asked by for the 1991 GMC Sonoma
Is it possible when transmission was replaced the exhaust is against the transmission causing it to vibrate and give you this "roar" sound
looked at that first, it's away from that....thanks for that idea