The sound from the speakers in my 1992 Jaguar XJS was very poor and also made a rattling noise when the volume was turned up.  I checked the front ones initially by removing the front door cards.  The foam cone supports had disintegrated, so I replaced the speakers with some identical new ones.  The rear ones also had the same symptoms.  I initially just adjusted the fader to only use the front speakers until I had time to examine the rear ones.

The easiest way to access the rear speakers first requires the rear arm rests to be carefully prized out.  There are 3 plastic pins that hold them in place.

This photo shows the 3 black plastic pins in the arm rest and the 3 white sockets that they push into in the panel.

I used a right angled metal bracket  and some vice grips to lever out the loud speaker panel.

3 screws hold the speaker in place.

It was then just a matter of disconnecting the old speaker, connecting the new speaker and reassembling the panel.