Engines on idle generally seem to have got louder since the 1980s. Pacers and Sprinters are quiet on idle, but it starts getting louder with the 158 and 159. Then 165/166 are louder still, then the Turbostar, and the 175/180/185/220/221/222 are the loudest. Luckily the IETs are quiet again.
In the case of 150s (and 153s, 155s and 156s) they are loud when accelerating but quiet on idle. 165s/166s are loud in both cases
(I miss them being my local units for that reason, but with the "normal passenger" hat on the electrification and 387s are an enormous improvement in noise).