Have a problem with a fairly new home on city water, water at kitchen sink pulsates when shower is turned on and gets worse as other fixtures are turned on. Shower will also pulsate as other fixtures are turned on. This appears to be an issue with main pressure since it occurs in both hot and cold water. It is not a tankless or on demand hot water system. I have found the only common in the system is a whole home water softner. I can not find a backflow preventer or a PRV in the system. Any help?

Push the By-Pass valve on the water softener and see if the problem continues... Back to you... Milo

Is this well water or a municipal water system?

Answer jlisenbes question and then bypass the softener as Milo suggests. Some softeners don't have a built on by-pass but three valves, (see image) to bypass shut off the two on the vertical lines and open the one on the horizontal side. Let us know the results. Good luck, Tom