It's a bit of a beater camera so I'm not entirely worried about killing it - although obviously it'd be nice not to, ha! I took apart the front part of the lens earlier on to give it a clean (there was a fair amount of dust kicking around on the rear of the front elements) an dwhile it was open gave the zoom mechanism a gentle blow through with some compressed air and this seems to have dislodged whatever small grit was causing the scratching sound!
There does seem to be a little friction still towards the wide end of the lever's throw, alas, which I am assuming is likely to do with the small rails this runs along being dry (I assume these would've been lubricated in the first instance, certainly the upper one seemed to have been at some point) so I shall have to try and find some suitable grease and perhaps give them a small dab... If that doesn't work then perhaps I'll have to dive in a little further.
Thanks for the advice, Dom! ☺️