I have a 1989 KLR250D5 low miles (7400). Over my 30 mile journey to work a rough noise started. I'll try to describe it.While riding at a steady low engine speed I hear a 'hollow' rubbing sound. At tickover (slightly irregular)a grating and knocking comes from the inlet cam area. Maybe camchain wear? or maybe the cam? or maybe something else completely? Oil changed regularly (semi sinthetic 10/40).Oil is clean. So far there is no noticable change in performance. The bike's not worth big money so I want to sort it myself and any help or advice would be much appreciated.

If the mileage is as low as you say, it's unlikely that the camchain has worn out. However, the Achilles Heel of many, many Japanese bikes was ( and amazingly, still can be ) the cam chain tensioner.
It is a very cheap job to check the tensioner, although you will need a manual. ( Part of the tensioner needs to be measured at certain piston travel to detect wear - but they often just stick, so don't run out and buy a new onw before cleaning as below! )Normally it's a case of removing it, recovering it in moly-grease or tons of oil, putting it back. Even replacing it shouldn't cost too much.
Does the noise go away after a long ride? ( Tensioners can stick or become lazy )
With a manual to guide you ( Haynes or Clymer are good ) I'd check and re-grease/set the tensioner. You should get a marked improvement in sound immediately. If you don't, let me/us know, and we can look at other alternatives. Let's hope!