Trying to find the cause of a knocking sound every time I go over a sharp bump. on 2005 Saturn Relay

Knock under the driver right rear section of the car and seems to "flutter" for just a second, but it is a loud knock. We thought the spare tire may be loose so we took it change. Had rear shocks change. I can actually feel it under the driver seat as well. Does not happen over speed bumps just hard pot hole like bumps...though middle seats were loose so took them out...not change. Sounds almost to be coming from the middle section of the car...visual check to see if something came loose underneath and nothing...very confusing. I don't think there is a rear sway there?
So this has baffle be and the guys at Brake Masters as well. Any ideas?

Asked by for the 2005 Saturn Relay
Also, IF it is NOT AWD the only thing under there that I can think of, that might make this noise, is the exhaust system! Is it All Wheel Drive?
not AWD
1 more answer
check your front strut mounts