I just got a central air unit installed in a new construction house.
The unit is mounted on the foundation wall on steel "L" brackets just below
brick level.
When the unit is operating outside it doesn't seem very loud but inside I
seem to be getting lots of low level vibration (even on the 2nd floor above
the outside unit!)
I've heard suggestions of rubber spacers between the unit and the brackets,
a rubber gasket between the bracket and the foundation, an extention on the
bracket to a triangle shape instead of the "L" etc.
Is any of this worth trying or do I really need to remount it on the ground?

The only issue with the ground mount is that my soil grading hasn't been
done yet so I would need to wait.
I also think I would need to go maybe 4 patio stones thick to get to the
same height as it is now from where I anticipate the fill level will be.
Any problem with that or is making a box filled with crushed stone topped
with one patio stone perhaps a better base than stacking patio stones?