converted oven over from lp gas to natural gas.Replaced gas valves, drill out pilot and burner orfices to proper btu rating.Gas pressure is at 3.5 Wc, burners are clean.My problem is when the burners ignite a low pitch whistle comes from the burner orfices.Double, tripled checked the orfice sizes and talked to tech support for proper size.Has any one ever ran into this problem with any gas equipment?