I just installed a Hansgrohe Thermobalance I in a new shower. Everything works fine when the temperature is set to either the hot or cold ends of the spectrum. The problem is when it is set some where in the middle ... you know ... where people actually like to shower. The water flow pulses pretty badly in this range. It seems to me that the valve is constantly trying to adjust the temperature and overshooting, almost like a drunk trying to keep his wheels between the dotted lines. Is this a common problem with thermostatic valves? Could it be a problem in the supply lines somewhere?

Thanks