A common source of noise (rattling, clicking and squeaking) is the rear seat latches, when the seats move the lock mechanism moves around on the latch and makes a noise. You could try tapping them with a hammer from above to bend the latch slightly downwards but this doesn’t seem to fix the problem in most cases.
To test to see if it is the latches making the noise drive around with the seats lowered. If it is the latches the simplest fix is to wrap some electrical tape around the latch where the lock contacts it to stop the movement and remove the metal on metal noises. The fix should last for around 50 operations of the rear seats before you have to reapply the tape and only takes a few minutes and a roll of electrical tape (3M Temflex 1610 was used but any quality brand is ok, avoid cheap brands) in any colour except for body colour or black as you won’t be able to see if parts of the tape are stuck in the mechanism or if the tape requires replacing.
- Lower the rear seats
- Clean the latch with a suitable cleaner (99.7% Isopropyl alcohol or similar is suitable)
- Wrap 14cms of 3M Temflex 1610 electrical tape (or equivalent) which will give you six full wraps.
- Close the rear seat
(the latches after cleaning, you can see where the lock mechanism has been contacting on the first photo)
(the latches after applying the tape, this is the area in which the lock mechanism contacts the latch)
(this is the tape after many uses, it should be replaced before it looks like this – I had started to peel it back prior to the photos)
(check the lock mechanism for any large stray pieces of tape that might cause problems with the operation)