I have just noticed my car has acquired a humming sound that starts to be noticeable at about 60mph, is at it's most noticeable at about 70/75, and seems to tail off at 80mph. I can't feel any associated vibrations.

The sound is definitely not the engine or road surface. I have checked tyre pressures but that doesn't seem to have helped.

There is a possibility a weight has fallen off my front offside wheel. All tyres were fitted at same place and the other 3 have those weights that clip onto the edge of the rim, whereas this one only seems to have a stick on weight. I can't say I noticed whether it had such a weight before though.

Any suggestions on possibilities? I was going to swap 2 of the wheels and have the alternate ones on the front anyway as 2 seem to lose pressure every-so-often.

Sounds like a wheel bearing on its way out. Jack up each wheel and check for play,on the rears spin them as fast as you can and listen for any noise

Could be a slightly distorted tyre too...

On the front nearside wheel, when it's in first gear, it moves back and forth in the direction of rotation quite a bit very easily. Could it be this one?

Apparently the rear nearside one was replaced due to "excessive roughness" nearly 2 years ago.

I've just swapped the two front wheels anyway (with what I think are the best 2 from my collection of 8 spares) so when I next go out I can see if that's changed anything.

Update: no difference with 2 new wheels at front.

If excessive play is found, is it worth attempting to adjust them using the Haynes manual method before taking to a garage to replace them? Or does noise = bearing death?

Just checked. Rear-offside, no play, but scraping sound when spinning. So it seems it is a wheel bearing. Thanks guys.

Other prospect is a "funny" tyre, where one wear bar is showing. I've had that happen to me once.