I would check that everything that needed to be removed to install the DP is back in and torqued to spec. It's tight under there.
I would take it back to who ever installed your DP.
Did some searching and couldnt fine anything specific to what i will try my best to describe. So most noticable is when i go into reverse. Initially it makes a loud clunking noise until the car begins moving then it stops ( sounds to come from right under the middle of the car, middle/front). Nothing like this in 1st from a slow start. But Another different noise between first and second when accelerating hard. As i go to shift from first to second theres another louder clunk inbetween shifts. It almost sounds as if my seat wasn't bolted down tight and was moving. But definately coming from under the car again, same spot...I just had a 42DD downpipe installed and i'm worried they maybe didn't tighten the driveshaft or maybe it's just the exhaust hitting? I am not sure, any help would be great. THanks