7.4.5 file write issue

We are noticing on our 7.4.5 system the following files are being written
approximately every 5 minutes

/tmp/.s.PGSQL.5432
/tmp/.s.PGSQL.5432.lock

Anybody know why they are being written? The reason I ask is because we are
running on a system that uses a laptop disk drive and requires at least 10
minutes idle time to spindown so it can recalibrate. This did not happen
when we were running 7.4.2, so does anybody have any idea what may have
changed between 7.4.2 and 7.4.5 to cause this to happen.

TIA
Chris White