Over the last few days I have noticed some noise under light to mid braking up to about 60kph.

 

It is a very light scraping noise - more like a "hiss" than a squeak. Braking performance doesn't seem impaired at all, it goes away (or perhaps I just can't hear it!) at higher speeds and if I do a full hard emergency stop, it seems to go away for a short period.

 

Is this signs that pads/rotors need replacing? I thought the 2016 vRS had sensors which told me when this needed doing?  The car has done just under 50,000kms and is running the original pads and rotors - is this a reasonable lifespan?

 

Could it just be some crud stuck in a pad? I can't see anything obvious in or around the brake gear...

It sounds like your discs probably have some surface corrosion. If you can't obviously see it from the outside it's quite likely on the inside face instead. Also your discs will likely have a raised lip on the outside and possibly inside diameters as well which would be rubbing on the pads. Or it could simply be a small stone stuck in the break workings somewhere and that is whats rubbing. 

A point worth mentioning, if you are a low mileage user (might take several years before your brakes are worn out) and run your brakes right down to the bitter end you may find that the protruding portion of your brake caliper piston will start to rust and not return back into the caliper fully without tearing the seal once you've fitted your new pads/discs. As your pads/discs wear down more and more of your caliper piston remains protruding. I don't mean to scaremonger there, it just cheaper to replace brake pads (within reason) than to repair/replace your brake calipers, particularly if you are paying garage bills and not going diy.