Even with our big fifth wheel trailer and diesel truck we learned not to worry about big diesel noises or any noises any more. First of all, we NEVER fire up the thing outside the quiet hours, and the second thing is we wear ear plugs which help that we can hear the noise A LOT.
I realize for some with thin-walled tent or adults with tiny children you need to listen for, this might not work well, but I'm throwing this out, just in case you can try this. We use those very soft disposable ones that you squeeze, then put in your ear, then they conform to the ear canal. They don't block out 100%, but they even help my very lightsleeper wife to get through noises like diesels. And they're comfortable to sleep with.
Fortunately, most diesel owners we've experienced pretty much are ready to drive off when they fire up their rigs so the noise doesn't last too long. I've heard of, but hope I never experience the idiots who do all of this in the morning so the loud engine goes on for a long time. I've heard complaints that even gas engines running for long periods can wake up neighboring campers.
Everyone, please consider this when you schedule an early departure outside the quiet hours.