When commenting on being flung about, hurricane, it was indeed stretches of the Cork line I had in mind, though the Galway line has several patches too where you experience, eh.... turbulence!
As railcars, despite my above comments, ICRs are the opposite end of the comfort scale to the ghastly 450, MED and MPD cars of UTA / NIR! All of them, particularly the 450 and MED cars, were extremely uncomfortable for any journey over ten minutes.
The underfloor engines on an ICR (or more so, an old AEC or BUT car) made their presence felt now and again, the AECs being even noisier than an ICR. But an underfloor noise-insulated engine is better than an above-floor engine.
Apart from diehard enthusiasts who like extreme engine noise (and depending on what's up front I'm one), travelling in the actual POWER car of a 70 or 80 class, or a 450, was sheer murder. I have travelled in all manner of trains on four continents and have never found anything with the vibration and noise levels of those. On a 450 the experience was added to by the two-speed engines (stop and start), the bad ventilation (warm and stuffy in summer, cold in winter) and the puny seats.
Rant over..... bah humbug!