My Mk1 vRS with 84k on the clock has recently started making a strange noise.  It's fairly quiet, soft sound, in time with the wheel revolution.  Most pronounced when cornering slowly, then as I accelerate the frequency increases to a quiet hum at high speed.
 
There's nothing obviously rubbing, nothing seems to be getting hot, efficiency is not affected.
 
Any ideas?
 

wheel bearings?

wheel bearings?

Could someone experienced in such things describe what failing wheel bearings sounds like?

Failing wheel bearings sound like a rumble that increases in speed as the car increases speed.

if the noise is louder when turning left then it is a right wheel bearing and vice versa.. the noise will increase as the load of the car puts more pressure on the axle corner with the failing wheel bearing.

You cant generally hear a wheel bearing untill you are above 30/40mph unless it is really bad.

Before assuming it is a bearing make sure the tyres are not misshaped or stepped as they make a similar noise. You can generally hear tyre noise at lower speeds + it will not increase when turning like a failing wheel bearing will

Saw toothed tyres?

I had serious wheel bearing-like noise and vibrations above 70mph and though something serious was wrong.

Replaced the nearly knackered tyres and all was right in the world again

Not likely to be the gearbox but does it happen in/out of gear. May be worth trying to coast in neutral to see if the noise stops, another thing to rule out. 

 

Most likely wheel bearings though, good luck.