Was out on routine service.Goodman GMS,this is single stage nat gas,hi eff. (sorry no Mod&Ser). First thing I noticed was,plate in front of burner brown in color,more burnt look than rust. Visually the burners seemed to be burning normal,however they have this "woop.woop.woop noise going on.Customer said he had noticed also.
I checked gas pressure,low pressure system. Had 6.4 in. 3.8 out. Adjusted to 3.5,still noisy. Noise the same,blower on or off.Have installed alot of Goodmans,I know this is not normal. Thanks ahead.