I am not that experienced on engine noises but I thought that the Pegasus on the Sea Harrier had a very distinctive noise on shut down. I went all the way to Yeovilton on their last day just to hear it. Actually, I was expecting a lot, lot more as well but was very disappointed.
I also miss the sound of a single Spey on a 1-11 using methanol injection and the curvature of the earth to gain height. And what about the distinctive whistle of the Goblin on the Vampire. Nothing like a couple of those doing engine tests to ruin one's hearing for good.