Had a 02 7.3 Ford. Everyone knew when I was coming - from blocks away. Forget out the volume in the parking garages. Pulled strong when I gave it up at ~170k. Great engine, alas the rest of the truck rusted away from it. Now the 6.7 Ford I'm driving now -- I feel like I driving a gasser in comparison. And the 6.7 is far more capable. Time will tell how well it treats me. Hoping as well or better than the 7.3 did.
Only way I've heard of the quiet a 7.3 is a "drive thru" tune from DP Tuner. I simple turned the truck off at the drive thru. In face it was so lout I'd hang back from the car ahead of me so they could communicate their order as well.