Do you have an expansion tank in your system? If not adding one of these should get rid of the pulsing. The expansion tank has an air bladder and stores a quanity of water at your systems pressure and will reduce
pump cycles and the pulsing. If you have an expansion tank the bladder inside it may be flooded or the tank needs pumped up with air. You can also make sure your showerhead is a reduced flow model.
Good luck,