Hi sorry for jumping in, I have the same sort of symptoms, I've a 2005 I-ctdi with 148k miles on the clock. Car didn't have a service history when I bought it though, but got it v cheap and thought I'd take the punt. I have another engine noise (posted yesterday on the 'engine clanking' thread.) so I don't think iv a rumble at neutral or in gear as it could well be the other engine noise.
My clutch is very long, in that to change gear it near needs to go to the floor, but the biting point is quiet short only a couple of inches and it bites. Especially noticeable for some reason in reverse. When the cars in gear and clutch depressed. Also say I'm waiting at lights and the clutch is depressed, it can almost stick for a second before jumping out and engaging, almost caused a few stalls. The pedal feels quite stiff too, and if in neutral and it's depressed about a third of the way I can feel your noise (if that makes sense) like a grumble, pulsating through the clutch pedal.
The clutch fluid is topped up although I can't be sure when it would have been last changed. Only had the car a month, there was no service history and the person I bought it from only told me about the work that had been carried out to it by her. I might try changing the fluid, although would be interested to know what signs to look out for if the master cylinder is on it's way out or knackered. Have also read people talking about greasing the clutch fork. Interesting write up on a thread ***led 'stiff clutch pedal' believe there's also a noise ***ociated which you'll hear from the right hand side - passenger side of the vehicle.