A few things I've found that can influence the arc sound level / noise in AC mode -

1. Arc length. Holding a tighter (closer) arc will make the sound levels lower than a longer arc at the same amperage and all other maching settings. A tighter arc will also focus the heat more, and make the machine not work as hard to welding at a given current level (reducing the voltage across the arc.)

2. Gas flow rate. Excessive gas flow rate will make the sound level too high. Try reducing the flow rate. If you are using the Everlast flow meter, remember it reads in liters per minute, not cubic feet per hour. If its set too high you could be drafting air into the shielding gas and getting oxidation in your welds too. So definitely look into this one.

3. Machine settings, such as AC Balance, AC frequency, pulsing. When I tried 50% AC Balance, I noticed the higher frequency AC noises were gone compared to say, 20% EP AC Balance setting. But of course you get a *LOT* more heat on your tungsten that way, and probably aren't going to get away with keeping a sharp tungsten tip at 50% AC Balance. It would be a big sacrifice to make just to quiet the arc.

In AC or DC welding mode, high frequency pulsing (say, ~300Hz) can make a "hum" sound. The "humming" will be louder the more dramatic the difference is between peak and base current levels. If you turn pulsing off in DC mode, the arc should get really, really quiet, almost silent.