Will I ever learn...

[JayDub]

On the A55 s/bound J19, at dusk, 75 mph, 4,000rpm, lights on..... Why is the volt meter showing 12.1v???
Turn off lights - 12.4v???
Is that a rattle I hear? difficult to tell with ear plugs.  Only 30 mins to home so I carried on, slightly concerned.
About 1.5mls from home I pulled in and removed ear plugs, GOD! - is it usually this noisy!
I decided that as I'd just done 145mls with ear plugs, it was best to approach this with fresh ears, so this morning I researched the DAR threads and decided that I should pull the alternater out for a look-see.
I found nothing loose or otherwise untoward  at least thats DAR eliminated, but why the low volts I wondered.
I decided to do what I should have done in the first place, and get the multimeter 
I checked across the battery terminals and saw 13.7v  I fired it up and saw 14.3v 
THEN I decided never again to buy one of those cheap (£1.89) chinese digital volmeters from ebay - even if they do look good grafted into the original Triumph clock 
And yes - it IS usually that noisy

[nickjtc]

Yup, the simplest answer is usually the correct one. 

[JayDub]

@ Nick -  (foul language)

[threepot]

Yes..Chinese! Hence my reason not to proceed with the 'aye' or 'ai mun' coils!!