The sound level will vary depending on the vehicle and whether you're running tailpipes or just to the rear axle, as well as H or X pipe.
SB Duster racecar with 3.5", X, Race Bullets, turndowns really isn't as loud as you'd think; kinda fun, since 6,000 RPM in the water sounds like 10,000. I'd say fairly streetable as far as loudness, but it's never street-driven.
Early B wagon, 440, 3", X, turndowns, deafening & boomy with Race Bullets & Dynomax turbos, finally the big Flows with tailpipes killed the drone & wasn't too loud. I'd call it rather loud.
BB Duster street car, 512, 3" with Flows & turndowns was LOUD at all times; Adding an H and 2.5" tailpipes, it's quite nice now but clearly audible from outside. Not as loud as the wagon.
Hemi RR, 438", 2.5", H with Dynomax Super Turbos, 2.5" tailpipes & modified tips, not too loud but markedly louder than stock.
I like a crisp sound but with enough bass that it doesn't sound tinny.