158's can be very noisy indeed, especially if you sit in the "wrong" part of the saloon. They also have an unfortunate defect of the rear vehicle often stinking of exhaust fumes.I can't understand this anti-multiple-unit prejudice that some members seem to have.
I can understand you not liking the noisy, rattly underfloor engines on a Sprinter, but that's not a problem with DMUs in general. Get onto a 185, Turbostar or even a 158 and the engine just a drone in the background - noticeable, but far from enough to wreck the experience of the journey.
Turbostars are quieter but lots of them suffer from rattly panels triggered by the engine.
The 80x underfloor engines are barely noticable.
Perhaps the 755 is the best compromise. Thrash enthusiasts can sit near the engine pod. People who like EMU traction package sounds can sit near or above the powered bogies and those who prefer the peace and quiet of loco hauled stock can sit towards the middle of a 2-car half set .