never saw a tranny shroud before...
vibrating shroud you are referring to might be a heat shield of the CAT or exhaust pipe or muffler.
IGNITION probs: if the owner sez he never had any probs-that subtly tells me that he hasn't done any maintenance on the ignition system either. SO... as a new owner, a good way to start ownership is to create a history of your own.
change plugs and coils. cap & rotor(when possible), and have the coil checked for integrity.
change ALL fluids... even when the previous owner sez he just changed 'em.
A/C... u can search the forums.