After normal start up with all burners sparking, all sparking stops as burner #4 (right front) ignites and is advanced past 3.5 knob position - if #4 knob is increased towards 4, left front and top right burners begin to spark? Consistent response ? Knobs 1,2,3 in OFF No other ignition - only #4 gas flow/burning? No apparent danger - only annoying noise. Any ideas how to stop unnecessary sparking? Thanks