1990 G20 Van AC noise

have a 1990 G20 van with an ac moan or buzz, the ac compressor has been replaced, the accessory bracket has been repaired, belt tensioner was replaced and all bolts checked for torque. The moan is most noticable with your hand on the high pressure line and resonates into the interior of the vehicle as a loud buzz. Any suggestion?

FCFFUZZYFACE