Grinding noise from serpentine belt area on TD5

So I was half way through a five hour drive yesterday when I noticed a sort of grinding noise coming from around the serpentine belt area. It only happens when idling and goes away when the revs pick up a bit. I’ve got the return trip to do today and I’m wondering if anyone knows if I’m in trouble or can I just go for it and figure out what’s causing the noise when I get back. I’ve got some Tec7 GT7 which is a multi-spray, I assume a bit like WD40. I was thinking about poking that through the grill and trying to give the pulleys a bit of lubrication but I need to figure out if that’s a good idea for something that I assume will get pretty hot.

Any advice?

Pop the belt off and run it for a minute or so and see if the noise goes or not. Would help to narrow down what’s causing it. Can spin the tensioner and alternator at the same time feeling for roughness
Also check the fan isn’t catching the cowling

If you're careful then a listening stick can help you pin point the noise. Just ensure you don't get it caught in moving parts or bad things can happen fast. A plastic cup on the end will amplify any noise so you can pay attention to the business end

Belt off and hand spin the tensioner & idlers pulleys, if one or more sounds like a roller skate you found yer problem, easy to change as well.
Could be alternator or water pump.... my vote is tensioner / pullleys.. (see my build thread for when I replaced them due to same noise)
You could try WD40 on the bearings, it will be fine with the temp of bearings but wont be a long term fix, in any event the bearings are closed so you are unlikley to get any into them, more likley to just spin it out and onto the belt.
DONT get any on the belt if it slips and your fan does not spin cooked engine...