I've used river rock, glass marbles and sea shells in my fountains for that purpose.

What sort of surface is the water striking when it hits the bowl??

...if it's just hitting the pool of water ... try adding some stones or pebbles to the bowl... build them up at an angle so the water flows down a ramp-like surface before reaching the bowl.

Put smaller stones in the bowl; they break the water falling into smaller areas.
You can also not put so much water into the fountain so the pressure is lower, or run the pump at a slower speed.

Can you turn the pump down or lower the water pressure? It sounds like it's coming out too fast.

Best of luck

Unplug it!