Among US-cert airframes I believe it is still the 747-200 (JT9D-3A) at an even 110 db on takeoff. DC8-55 was a full 4.5 db quieter! Also interesting to note that the Sabreliner 60 is one db louder than the LR25 and more than three db higher than the 24D.
All things being equal, of course, which they never are, of course. The DC8 sure seems louder than the 74, and I would have bet that the LR25 made more noise than any Sabre...