There's a squeak noticable when driving slowly (town traffic), that disappears when the handbrake is applied very lightly. Handbrake works 100% and settings (1 - 1.5mm from stop) are fine. Is there a shim or something that needs attention?

I'll take the calipers and pads off if necessary but any advice would be welcome, especially since it seems I need to replace the guide bolts once removed (Haynes Manual). Why?

Which model of Octavia is it? There are 3 different rear brake arrangements dependant on trim and engine.