Noisy motorised volume pot

In common with my recent theme of hifi breaking/playing up the motorised volume pot on my Marantz PM7000 has recently started making a rather worrying grinding noise as it moves towards the quieter end of the spectrum

The motion of the knob (ooh err) is still smooth, just its a bit noisy as it turns. If I turn the volume up it moves fine and doesn't make the grinding noise. I could take this as an excuse just to keep cranking up the volume but I'd really rather just fix it!

I'm presuming something needs lubricating - I'm unfamiliar with the insides of the amp especially the volume pot part, so I don't want to start spraying PTFE grease or WD40 or whatever I'm supposed to use around willy nilly! If someone could give me a quick run through of what to try that'd be great - can take some photos of the innards later on this evening if it'd be any help!

EDIT - To clarify, its a mechanical grinding noise and not coming through the speaker as static or anything like that!