Just had both rear struts replaced and am still hearing noises when driving over any size bump. Noticed just now that
each strut boot (plastic covering?) is loose and easily moved. Should these boots be so loose?

 

are you referring to the cover for the nut on the strut rod that holds the upper spring seat to the spring? If yes, can't see it being a problem. make sure the strut rod nut is tight.

do you have a rear sway bar? the links can wear and clunk over bumps.

 

All seems tight except for the plastic(?) sleeve that fits over the strut. Others I've seen are rubber and fit tight; this sleeve you can move up and down and
seems to be the source of the noise. Not sure if it should be so easy to move, or if it's missing something to keep it in place.

 

pics..