I think the sound of a Beaver or an Otter taxing into a dock on cold fall morning is one of the best sounds in aviation.
Years ago I was sitting in a S-58 while the pilot did a run when parked next to a highway. Looked outside to see a bunch of HD bikers stopped by the road.
They were fascinated by the sound.
After we shut down they wandered over and when we opened the cowlings they saw the engine and one of their number said "It's the mother of all Harleys!"
We directed them to the park next to the busy float plane base which was full of Beavers, Otters and even Norsemen. We passed by a couple of hours later and they were happily sitting there just basking in the noise.
Of course the sound of an Canadair Argus ( Canadian Anti sub 4 engine ) at full throttle during a low pass is a sound never to be forgotten.