Hallo,
first of all we need to clarify a few misunderstandings.
when you have a buzz or any other noise you have riple or oscilation or somehting and you can see this either with a multimeter when it is a buzz and measure ac voltage. Or with an osciloscope if you have sound sof what so ever due to oscilations.
when we have dc offset there are NO sounds. You can see this on the woofer when it moves in one direction. This is DC offset and can damage your woofer when it is excessive. A few millivolts are only good. maximum maybe 50-100 mV. I would say less then 70mV.
The best is to match the mosfets or trim the dc offset changing the resistor that bias the FETs till you have 0mV at the outputs.