This issue seems to have materialised in the last few weeks, and to be getting worse. It is periodic/intermittent, eg occurring on & off during perhaps 1 single hour of the day, possibly more, sometimes less.
It manifests itself as a pulsing buzz or drone through the speakers, sounding rather like the effect of a mobile phone in close proximity (just before it rings or receives an SMS). Accordingly I switched off any mobiles in the room, and checked for any others nearby (eg within 10 metres). No change, problem remains. Beyond 10 metres I really couldn't be sure what's in the vicinity, or realistically control it anyway.
Next steps. Switching off the NAC92/Flatcap stops it, with the NAP still powered up, so it seems to be something affecting the NAC. Then I disconnected every input cable. No change, problem remains - so I think I've eliminated a source related issue.
Other options. It would seem it must be either airborne (RFI) or mains-borne. I tried powering everything through an Isotec MiniSub I had lying around. No change, problem remains.
So whilst I'm far from sure, it looks to me most likely an airborne problem. But:-
a) what could be the root cause ?
b) how is it entering the NAC ?
c) what possible remedies could be tried other than what I've done already ?
Really appreciate any thoughts & suggestions as its driving me nuts ! :-(
Posted on: 07 October 2015 by Simon-in-Suffolk
Ok if not a neighbour and on your wiring - its is quite possible the washing machine is creating significant interference on your mains voltage. If the suppressor ( capacitor) has gone open circuit or been disconnected this most likely would happen. In the old days of analogue TV you would see sparkles on the TV screen when this sort of thing happened.
Might be time to get a new washing machine!! If its as you describe I am afraid ferrite chokes are completely the wrong tool for the job and most likely ineffective.
Simon
Posted on: 07 October 2015 by karlosTT
Our new Meile cost a lot more than a Nait, and weighs more too at 101kg.
Well, for every rule an exception HH. I'll wager it doesn't sound as good...... ;-)
Posted on: 07 October 2015 by Mike-B
Originally Posted by karlosTT:
But seriously, how/why does it weigh so much ? It's made of lead ?
All washing machines have large lumps of weight, normally a form of concrete, inside to help damp (stabilise) the loaded drum unbalance oscilations with in spin cycles
Posted on: 07 October 2015 by feeling_zen
That generally applies only to European front loaders which fairly rare in many countries.
Most washing machines in my neck of the woods are just about light enough for one person to haul up a flight of stairs. And many only use cold water too.
Posted on: 15 October 2015 by karlosTT
Well, time to round off and close out this thread.....hopefully.
The good news is that this problem seems to have disappeared completely, as mysteriously as it appeared in the first place.
2 day tests with the washing machine on/off actually seemed to eliminate this from probable cause. I therefore come back to my original feeling it was a form of RFI, from source(s) unknown and unidentifiable. Which has now evidently gone.
The other possibility was a form of external mains borne interference, ie on the grid supply rather than generated within the house mains. If so, then that has also cleared itself up and reverted to normality.
All in all, a very strange and peculiar escapade which leaves me baffled and mystified. On the other hand relieved - that blissful quiet has returned (touch wood).....
Posted on: 16 October 2015 by karlosTT
Dammit FeelingZen, you may have hit on something there. Chariots of the gods ! ;-) I am going round to the neighbour's banana plantation to look for crop circles.....
Truly odd stuff, really. Kind of shows how vulnerable a hobby like this can be to the vagaries of science and the environment.....
Posted on: 16 October 2015 by Simon-in-Suffolk
KarlosTT, just a thought, it sounds like you live in farming country... The same as I, one of the things that does happen from time to time that does cause occasional audible RFI are electric fences with damaged insulators, poor energiser earth connections, or some sort of vegetation discharging the wires after rain etc... Before now I have wondered around local fenced livestock fields with the appropriate farmer with a LW portable radio narrowing the issue down. Luckily in the UK the fence operator is required to resolve.. but I have never had any push back.
Posted on: 16 October 2015 by karlosTT
Its a thought Simon.
I can't off hand think of any electric fences nearby, but for sure all manner of DIY cabling and even dodgy "official" cabling exists all over the place. Some of that could have got submerged in say rice fields, and been shorting out, causing a similar effect to what you describe.
There are probably 101 myriad scenarios, and whilst I'd like to think its a lesson learned, I'm not so sure its actually quite that positive ! Feels more like a hostage to fortune.... ;-)
Posted on: 16 October 2015 by Huge
Originally Posted by Simon-in-Suffolk:
KarlosTT, just a thought, it sounds like you live in farming country... The same as I, one of the things that does happen from time to time that does cause occasional audible RFI are electric fences with damaged insulators, poor energiser earth connections, or some sort of vegetation discharging the wires after rain etc... Before now I have wondered around local fenced livestock fields with the appropriate farmer with a LW portable radio narrowing the issue down. Luckily in the UK the fence operator is required to resolve.. but I have never had any push back.
Simon, that left me with an image in my head...
of 'The Hood' aimlessly wandering around a Suffolk field with a portable transistor radio!
Quite magical really!
But then again, I suppose my avatar may lead people to think of Guido Faulkes listening to 'The Music for the Royal Fireworks' and thinking...
"If only, if only..." 
