Weird vibrating creaking sound under my car?

So recently i put back on the stock exhaust to my honda civic, i put it on correctly and it fits snug up against the chis like its supposed to. But when i take off from a stop in first gear it creaks really bad and i can feel it vibrating right under my seat in that area. also when i make turns (right and left) it creaks really loud, and it vibrates also. Can anyone tell me when my car is doing this? And its not just the exhaust, its the whole piping from the bottom of the headers to the back, but the part that creaks is right under my seat around where the cat is.