1998 Mustang gt suspension question

i have a 98 gt and i have a banging noise underneath the car its bin there for 3 months now and started during my first run down the 1/4 mile track rite after i added a full exhaust headers back it appears to me that the exhaust is hitting the rear differential a little bit but only enough 2 trade paint there is no dent of any sort in the exhaust and i think the noise is something else because the car now jerks around with the cruise control on wen going down hill and my cat efficiency engine light keeps coming on, i had all my rear control arms and bushings replaced and upgraded i replaced the transmission mount and nothing is fixed


my rear control arm bushing which are brand new and polyeurathane are coming apart in the very back but the others are all solid so my rear differential has to be moving around under there



i was at my uncles repair shop today and he suggested new rear shocks and replacing the bar that connects to the shock but runs parallel to the ground and looks kinda like a strut does anyone no wat this piece is called? any suggestion on rear shocks wat company to use?



does anyone have any other suggestions as to what could be making this noise has anyone ever encountered this before?