I wish I had your hum problem @Antony
I’m currently powering my 282 with an aftermarket half-size power supply. Can’t wait to move it on and get a humming one 
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I used neoprene tape 40x4mm the sticky back stuff it’s cheap and widely available. It’s a good idea not to tighten it down too much either.
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However, I wonder if it is worth buying an Audiolab Dc Blocker (perhaps even the 6-socket one).
I had a DC blocker in my system for a few years. At no point did it stop transformer hum.
in hifi unfortunately everything is the opposite of everything! I should give it a try and buy a dc blocker to test if it works on my hicap. I know of people who, after 6 months of eliminating electrical hums with DC, have started to feel them
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Please I ask you to clarify for me whether it is useful to also connect an AD block to the amplifier, the CD player and the streamer even if the last two, as is well known, do not have toroidal power supplies. However, the connection, for example, to Ad block 6 Audiolab, could be used to clean up the spurious currents in the home network. What do you think about it? The Audiolab dc block 6, in proportion to the single ad blocker (both Ifi and audiolab) is cheaper having 6 outputs.
As has been said on many threads, diagnose the problem accurately before deciding on a solution. A humming transformer is not the problem it is the symptom.
As such there are several reasons that transformers hum and DC offset is not the most common issue (though audiophiles seem infatuated with this concept). It might be the issue, but could easility be over voltage (is more common than persistent offset), or a faulty winding.
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Out of curiosity, why is it that, in my experience anyway, problems with humming transformers is common with/unsurprising from Naim power supplies. Since the early 1980s I have only experienced this phenomenon once…with a HiCap.
Beats me. I’ve never experienced it. Touch wood.
…and, that’s another interesting point: why some, but not others?
Not worrying about transformer hum is a very cost effective solution… 
Or - just try another sample of the same Naim unit - say by borrowing one from a dealer. If its better, fine - maybe get it swapped. If its the same, just (try to) stop worrying.
Some Naim’s Hum.
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I polled this a while back here: Naim Transformer hum (or not) to AC mains type poll
Sadly didn’t get the results back in numbers sufficient to draw meaningful conclusions. I have a theory that the transformers (which are the same for both 115 and 230v just bridged differently) are more likely to hum as voltage increases beyond 240v.
As to ignoring hum, I wouldn’t unless very quiet. Toroids are chosen for their low EM radiation compared to other types and hence are rarely shielded because the flux is confined to the core. But an obviously humming toroid means it’s saturated and a saturated toroid behaves worse than anything. Then you have and unshielded core showering EM radiation well beyond itself and the whole reason it was chosen in the first place is nullified. It will be impacting other components in the vicinity.
One argument for EI core transformers is that although they need distance and shielding, their performance is very stable under both good and bad mains conditions. Toroids are not forgiving.
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Naim philosiphy is about good power supplies, and with that come large toroidal transformers. The problem is the toroidal transformer, and not Naim specifically is my understanding. Some people with non-naim gear which use large Toroidal Transformers have commented on similar issues in the past. So this may explain it
Toroidal Transformers are adversly affected by over voltages, and also DC offset for example, and of course these are going to vary from house to house, hence some experience it more than others.
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I would recommend investigating hum, first. Trying another HiCap in the OP’s case, should not be difficult.
Its is known that some samples of Naim PSU’s hum more so than others - there is a known variation. I believe Naim test them when received and reject the worse ones.
Checking the incoming mains is another on the list, if you have a ‘hummer’. Again, people have posted on here about over voltage and/or poor earths on their mains, which - when addressed, reduced the hum they had.
Peoples perception will vary. How loud is the hum - at what distance can you hear it…? If its only when very close, I think that’s normal. If its across a room, that’s not.
Very much YMMV… 
So I would conclude from these statements that the hum is possibly inevitable. If only there was another way! 
…are these frequency specific?
You have to swallow twice as many below 100Hz 
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Solved then!