The cycling of water between your tank and grow bed will create some noise. You can soften the noise by keeping your tank topped off with water to ~1 inch below the growbed. You can play around with the water level but just be sure to leave a gap so your fish can swim to the surface and breathe. 

Also, if you recently re-planted this can effect the sound your water makes. The roots of the plants help muffle the sound of the cycling water so if you just re-planted it's normal to have a louder cycling sound.

If all fails and the sound is still bothering you, go ahead and unplug the pump. It doesn't need to run 24/7 so you can unplug it during times that are most bothersome.

Hope this helps and let us know if you have any additional questions.

Happy Water Gardening!