Dude you are in DEEP SHI............................................... .TT
you're looking to a $3,500 USD job let me tell you why and Pray to God this is not what happen to you
You must own a 92 to 95 325i the E36 chasis it's known to be weak on the rear sub-frame mouts plus lowering and hard driving your car will make even worse.
there are 4 mounts on the sub-frame that holds the differential in place the passanger rear side is the first one to brake or rip off form the body of the car then the front one and then the driver rear and the last one the driver frot and then the dift is on the ground.
what you are hearing is the mount going in and out of the body or frame of the car
park that bitc*h get her on an jack and look underneath and check for damages.
now if this is it......
go to WWW.TURNERMOTORSPORTS.COM
and buy the rear subframe reintforcements and then take the hole undercarrige apart (exhaust, second pice driveshaft, wheels, differential, lose your calipers and make sure there is no fuel on the tank) the polish the subframe and repair the damage and then 360 digree weld the reinforcements then pait the subframe with undercoat spray and puit all together.
if you wanna keep driven her hard get a 4 point rool cage to stiff the rear end of the car so it won't flex at much and it will not happen again
Good luck dude and
I will be praying for you.