At first reading, it could be a clutch release bearing.

If it is that, then the only thing you can do is make sure that you drive with what is known as 'mechanical sympathy'. Even then, whether you'd extend the life of it is debatable.

An alternative might be something in the gearbox, and to get the gearbox oil changed. But make sure the garage REALLY know what they're doing if you consider that, because too many manage to screw up that sort of job, it's not as easy as changing engine oil.

Apart from that, there's nothing that you can really do to avoid whatever is wearing out from wearing out. But it could keep on going for another 100k miles, or it could break down next week. However, if it's a faint noise that's not getting worse, then more likely to keep on going for quite a while.

No matter the "official" line about filled for life from the manufacturers (PS I am an engineer at one such), in my book 90k is way too long to go without a change of oil in the gearbox. So, this would be my first port of call.

I'm a fan of Castrol Syntrans - fully synth and resonably priced at about £12 a litre. It quietened my box down quite a bit and massively improved the shift quality, especially when cold. It may be a false impression but it also feels like it's letting more power through too once it's nice and hot.