2005 sonata

2005 sonata 4 cyl shakes pretty bad when stopped and in D. When its in N or driving no problem I recently had to change the steel flex in the exhaust pipe and there was a hanger just before the steel flex I could not put it back (rusty broke)I wonder if this is the reason its shaking so bad (it always had a shake you could actually see steering wheel shaking)or are motor mounts getting weaker does anyone have any advice