As for the "bump", don't know what else it could be, there aren't any obvious hills there.
Silbury Minor (Silbaby), or one of the Seorfon Barrows opposite the Sanctuary on the Ridgeway? Or have I got the wrong direction?
Yes wrong direction Ocifant. You'll notice the church at Avebury just to the right of the 'bump'. Silbaby would be to the rear of Silbury Hill on the right of the drawing.