I currently own two Triumphs, one 3 cylinder 955i & one 4 cylinder carbed 1200. the 3 sounds sweet, the 4 a bit like a tractor when on tickover.
It was explained to me once that the 4 cylinder engine is basically a 3 cyl one with the 4th cylinder tacked on to the side, physically as well as electronically, which is why it sounds odd.
Once on the road though & the 4 pulls like a train & while not as sweet sounding as a Bird (not many bikes are), still sounds good, especially with Delkevic end cans.