There might be something wrong that is causing more vibration than normal,
but more likely you just aren't familar with how it sounds and it is
operating normally.  The high speed fan, as people have said is very loun
and spins fast so you can feel it a bit by your feet even when driving.  The
noise you can hear at any speed as you noticed.

The only other thing I would add is if all is well, your high speed fan
should (almost) never need to kick in.  Maybe up a steept grade in heat with
AC on.  So, might be time to start thinking about some regular cooling
system maintenance.

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