Some pleasant memories on this thread!
I'm old enough to remember hearing B-36s in Eastern England in the 1950s. Unmistakable even if I didn't always see them. And the few times I did see one it seemed very low, but that was probably because it was very big! But maybe it WAS very low too.
Laurence

The RB211-535C fitted to the first Boeing 757's made some horrible noises! I remember taxying into Malaga Airport in the early summer of 1983 with both engines making a terrible noise. As we stopped next to the terminal a massive plate grass window facing the ramp shattered.

Griffon Growl
The Yowl peculiar to the Vulcan.

Capt Chambo has it for the Concorde (used to set off the alarms in Cranebank carpark, daily),throttled back Merlin also very distinctive, but the "couldn't mistake it, even if you couldn't see it", was, as I.garey says ... the B36 - quite unmistakeable; to me, reminiscent of a big, slow turning motorbike.

When you have experienced the sudden and unplanned silence in a four jet at 10,000 feet above N. Atlantic any engine sounds good.

P&W R1830s fitted to the DC3 which rattled like a mechanical coffee grinder during stat up.
RR Spey fitted to the F28 which caused the terminal windows to vibrate when it taxied in.
Garrett TPE331 which when fitted to the SA227 projected noise forwards well as backwards.

Three airplanes I could and still can always tell :

- Piaggio Avanti
- MU2
- DA42 with Thielert engines.

As far as music to your ears, it’s nothing like a big piston engine going at full bore.
Not a big fan of jet engines unless it’s an afterburner take off although some sound better then others with full A/B.

As a ramp worker always enjoyed the pushback and engine start of the last of Delta’s L-1011.
The spooling up followed by the clicking of the igniters then the WHOOSH when the burners lit and it truly came alive.
Modern jet engines seem to lack that.

My favourite was the P&W JT8D crackling on an early cold clear morning T/O from YMEN from 727 or DC9.
TPE 331 also a standout depending what airframe it was fitted to, the MU2 particularly
Merlin just fantastic.
RB211 on Tristar start and initial spool up on T/O

Just to get the facts right. The BAC 1-11 used water injection to boost thrust, not water/methanol.
Are you talking about a single Spey after an engine failure?
About 1981, I was living in East Grinsted and a Laker 1-11 lost an engine on take-off from Gatwick about midnight. The noise of one engine on Max power for about 10 mins. as it completed a circuit must have woken up all of Horsham, Crawley, East Grinsted and most of Sussex.

As for the most notable sound, how about an A400M.
But the Merlin does it for me.

dixi188 I stand corrected on the methanol injection on the Spey. I am talking about EFAT during crew training at Hurn. I worked about 6 miles from Hurn and, when a 1-11 with one engine came overhead, it was still quite low and very loud. On at least one occasion, the largely female workers in an enclosed clean area panicked and started to rush out of the door.

Much later on, I was chatting to someone outside the BA Engineering Building at Heathrow and heard a similar noise from something taking off. Thinking it might be Concorde I rushed to a gap in the buildings where I had a glimpse of the runway. It was a 1-11 and,even with noise reduction kit, it had that ear splitting noise I used to hear so regularly at Hurn.

The GE90-115 on the 77W sounds like a beam engine when starting.....clanking and banging away until it settles down

Perhaps it was because there were 3 (harmonics?), but the RB211's on the Tristar sounded just perfect

This summer, when temporarily back in the UK from my home in SA, the two distinctive noises that always made me look upwards were the haunting banshee wail of the A400M's heading into or out of Brize, high over my house near Bracknell and the earth rumbling drone of An-12's steadily plodding their trade on the airways

It is of course a sign of the times that a pair of Pratts, GE's or Rollers on a modern jet are remarkable only for their quietness, particularly the A350

Oh, the most charismatic aircraft engine sound just has to be...
Jet noise, the sound of freedom

I agree with you on virtually all of those, perhaps a generational thing and having a great interest / involvement in commercial than military aviation. However I'd add to the list the Ivchenko AI-20 on the IL18 and AN12, used to love hearing the sound of them on TAROM IL-18s when they used to operate the Balkan Holidays charters to Constanta, and of course they've made a comeback in the last few years with the number of AN12 charter operators frequenting the UK. There always seemed to me to be a distinctly less raucous scream from RR Darts when there were only two of them, and mounted on to F27s and HS748s. I always preferred the Viscount for noise.

The most iconic jet engine sound has to be the JT3As and JT3Bs strapped to 707s and DC8s before some Philistine reengined them with CFM56s. The sound immortalised on the Beatles "Back in the USSR" track.

Merlin, hands down. Spitfire, P51 - just a beautiful sound.

I have never heard it but apparently the sound of a B 36 with just six turning was an Earth stopper.

What about the XF-84H ‘Thunderscreech’?
It may not be considered a charismatic engine sound however it was certainly loud.
Apparently ground crew became sick from the sound waves created during ground runs. It could be heard from 40km away.

Don't talk to me about Griffons. "Eh, what did you say?"

How about the RR Tyne?

The AN-22 is certainly very distinctive...