It is a DIY fix. Most likely you are leaking air out of the small vent hole on the side of the Pressure Maintaining Valve. There is one 90 durometer 004 sized tiny o-ring that likely needs replacement. It's either that on or the two 010 0-rings inside. Don't order 70 durometer or they will blow out under pressure. Here is a cross section diagram of the PMV with parts identified