gas milage change & thump noise

What is your question?

my Jaguar was getting 19/city 21-22/hwy now I'm ony getting 12-13 city/hwy, with a slight rough idle, plus on my right rear i have a thump and knot as if somethings loose I,ve had it on a hoist to check shocks but every thing's tight, could it be a bushing?