As an enthusiast, personally speaking, when it comes to wibble I'd put thrash and noise before paint and clag
.....but we're all different
But seriously, I agree, a Valenta powered HST is quite possibly the noisiest train I've ever stood next to went it starts up, and in this case it's the screaming sound more than anything else. I noticed recently how much quieter the re-engined ones are (are the LNER ones MTU? I can't remember).
The other thing I've noticed recently from watching a lot of older videos of 80s traction is just how smoky/claggy/dirty (or however you want to describe them) older diesels really were. I don't remember them like that myself at the time but in every video, everything smokes and clags. In comparison a 68 is a breath of (slighty) fresher air.
I do think the 68s are the best sounding modern diesel, and for this enthusiast, sitting in the ironically positioned quiet coach (1st one behind the loco in a Chiltern set) is quite fun. Having said that I imagine that as we have far fewer diesels locos around these days, the minute we get one that has a bit of noise about it (let's face it, 66s aren't anything like as loud), it does rather stand out. Places like Liverpool Lime St mentioned above or Man Vic, and many others are now home to more electric trains than ever before, or somewhat quieter DMUs and haven't seen diesel loco hauled trains in some time. People will have got used to a lot less noise.
Just my opinion anyway....