A lot depends on the generator I will list 3 types
"Contractor" Open frame 3600 RPM are LOUD!!! Earplugs should come with them,
How loud they will be in a Wal*Mart lot I do not know but I'd not want to park near you for the night (Been there done that)
My Onan 5500 Emarld Gold.. IN the average Wal Mart lot you will not even hear it (I do use a Gen-Turi which changes the nature of the sound a bit) but it's hard to hear.
Honda Eu200I or yahama EF 2400i. THese are INVERTER type generators you may need two of 'em in parallel to run the A/C
Some years ago a friend and I were talking to a Yahama salesman at a rally We had 3 generators in front of us 1200, 2400 and 3600i models.
THe 1200. I could not hear over crowd noise at no load.. I could feel the exhaust against my ankles but not hear it.
The 2400 I could hear but my friend could not.. (I am used to hearing sounds under noise so was able to "pick it out")
the 3600 I could hear but no need to raise our voice.
At half load, no significant change
At full load the 2400 "Spoke up" and coudl be heard clearly.