I couldn't hear a whistle sound just the burner. But the sputtering of the flame is not normal. It should be steady. You might try adjusting the sliding air tube to see if the flame evens out. If not I would look at cleaning the gas valve. There are several u-tube videos on the how to clean the valve. or have a propane dealer clean it but a new valve might be just as cheap and quicker.
Glad you at least got it to fire up and give you hot water.
Doug and Sue.
07 Diplomat 40 PET
2011 Jeep Liberty pushing.