I also encountered a rattling sound on my P1S.
After checking the fan thx to @Heliguy71 I found that my screws where not actually holding the fan in place. There was a gap and the screws seemed to not want to be screwed any further. I used some tiny washers I had lying around and they seemed to have fixed the problem.
If you have a similar issue but no washers, just print some.
Mine are: 3mm inside - 7mm outside - 1mm height.
