Denford Software & Machines

I am in need of a little advice.
My vmc 1300 developes a clicking noise from the spindle area as the head heats up on a long job. When it's cooled down its smooth again.
Is this a serious fault?
I can't see a grease point anywhere, bearings and belt are hidden inside the castings.
Are they tapered bearings requiring adjustment?

Update on my spindle bearing noise, with advice from Steve at Denfords I have now changed the main bearings and after the first run it seems to be nice and quiet.
It took a week of careful work, made a few special tools and pondering how tight the bearing tension nut should be , as it will take a few hours to
get at it for adjustment if I have got it wrong.

My VMC1300 Pro has just developed the same "ticking" noise from the spindle after it's been in use enough to warm up. I fear I have to go through the bearing replacement process too. I have the spindle section drawing posted in the drawbar thread, so I can see generally what's required. I have a lathe and manual mill, so am up for making some special tools. I'd rather make them before starting to pull apart the brute, so I'll request some more info and pricing on new bearings. I guess I replace the belt too, as a matter of course while it is apart.