Mentioned over on "spotters forum" that on Tuesday morning I heard a distant and familiar whopping noise while walking through some local woodland and surmised Chinook - check on ADSB confirmed it was indeed (apparently there were actually two) some 15 miles away over Park Royal in West London, heading south towards the Thames heli lane. Even allowing for me being on the highest point in Croydon, reasonably divorced from traffic on a nearby main road with (had there been no trees) a clear line of sight and a favourable wind, I was quite astonished that the sound could carry across the bulk of London and all the ambient noise of a weekday morning.
(Always used to amuse me that on the reality Cop TV programmes when the Met Police's "India 99" EC-145 was being used for tracking suspects on foot, the voice over would breathlessly announce that "they have absolutely no idea the chopper is there!" Really? They must be
deaf then as the EC-145s, (and the earlier AS-355s and Bell 222s) are very audible from miles away - having had the things orbiting my area in the wee hours on countless occasions, I'd be amazed if many locals were still asleep.)