They are noisy in the first few rows nearest the power unit. But then they aren't at full throttle for very longWow...stunning acceleration in diesel mode. 0 to 60mph in 57 seconds. 0 to 90mph in 121 seconds. The new king of diesel performance!!
And sorry to say it but the noise of those 4 no V8 Deutz diesel engines - however glorious - is very noticeable - intrusive in fact - on full chat when sitting in the seats nearest the power car. Nowhere near as silent as the coach nearest a HST power car

I'd say the middle to far end of the coaches next the power unit are akin to first coach in an HST or loco hauled stock. Outer carriages are like being on an EMU.