I have a new rudd air handler and 4 ton compressor, when the unit turns off there is a slight grunt noise. Installer says there is an electric brake on the blower at shut down ,this sounds good but is it true noise is not very loud ?

If you have a variable-speed indoor unit, the sound you hear is not unusual. DC motors have much stronger magnets than AC motors, and a pulsing sound at start-up & during coast-down is inherent to these types of motors.