It sounds to me that your new pump is moving more fluid than your old one.
I'm no expert on pool pumps, but I've worked on industrial pumps for 25 years. When a pump sounds like it's got gravel in it, it is starving for fluid. It's not air in the line. Air doesn't make any noise by itself. If the suction line is not flowing enough water to the pump, then the pump gets loud and sounds like it's got gravel in it. The term is cavitation. It means that the intake line is partially blocked or too small for the pump.