That is a rather low temperature rise for a gas furnace. I would
suggest dropping the blower speed one tap. I would normally expect to
see between 40 and 60 degrees temperature rise with a gas furnace. See
if the installer can do that for you.

BTW, the fan switch on the thermostat should be set to AUTO. If the
switch is set to ON, you would be running at air conditioning speed.
But the grilles should still not be that noisy.


Stretch