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.