have it checked out.
That model is supposed to turn off completely to allow the pressures to equalize before the compressor turns back on... The timing is around 30 seconds so that is good....
Have them check to start components for the compressor as well as charge and whether the pressures are equalizing like they should. Definately not a normal sound....
Does it make this noise when the unit starts in heat or is this only a defrost issue?
I fully support the military and the War on Terrorism.
If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.
If you do know, then do. But do it right. Otherwise, you may not be doing it long.