Annex14, ref your post #22, as you stated, on approach aerodynamic noise is the killer.
I used to fly for a company that had a limit for geardown @ 3.5nm, sometimes a bit late to use as a target versus limit, and certainly only usable if one was applying the 500' VMC stable appr gate in preference to the 1000' IMC one.
It was always nice when flying a visual to try to leave the gear till that point & be spooling up @ 500 agl if possible just for self satisfaction (to the naysayers who say too late to stabilise I would say, well, a CFM56 is permanently spooled up anyhow, so response is pretty much instantaneous from the artificially high flt idle we have)
I had the good fortune to fly many visuals over the city I lived (no noise abatement/local regs to prohibit it, and I am sure the local tourist board liked it
) following an sms sent from 8000' ft or so to Mrs Playstation to look out.
I always asked afterwards, "was it loud" as we arched gracefully across the centre @ 1500' or so agl in a turn, apparently it wasn't, but on the days when I judged it less well & passed above 1500' but with the gear down it was, I am told, much noisier.
So (and good airmanship does sometimes dictate otherwise) the key to appr noise appears to be the latest practical selection of gear (following a well executed CDA ) On take off I am sure thrust reduction@ 1500 accelerate @ 3000 in reduced climb would be the best, but , the need to save fuel/engines has won the day here in most companies priorities, witness Ryanairs change from NADP1 to 2 as the default choice.