I have a dolly cart at home the same height as the truck bed so I can slide the Honda 3000 in and out of the truck from/to the dolly cart. While camping it stays in the truck.
Noise depends on direction of the exhaust as stated above, and also what it can bounce off like the back of the truck's cab. IAW it varies.
A 3000 running the same load should be quieter than the 2000 just from not being revved so high out of its max revs. Two-2000s running that same load should be quieter than the 3000 except there are two of them, so no idea how that would compare.
the 3000 has a lower frequency sound that is easier on the ears than a higher pitched sound. That might be what is going on. Not sure what a 2000 sounds like anymore for pitch, been a while.