Here by London City the Flybe and Luxair Q400s are the most noticeable of the turboprops. From inside the house I notice their noise on departure where I don't notice any of the other turbos (we even have the old VLM F50s back) on the same track.
For all the reference is to engine types, most of their noise comes from the prop tips.
I think that LHR should have used the idea of reducing stacks as an important point and would play many at their own game.
The real
PR error was just closing their onetime third runway 23 as not required, having made its use as awkward as possible in the years before. If they had presented the whole thing as a runway "realignment" of 23 a further amount of opprobrium from the general press and public would have been neutralised.