‘… other noises were mingled with the chakkering.’
In this form, I couldn’t find this word in the OED, but assume it might be related to ‘chack’ and ‘chacking’, a mainly Scottish verb meaning: ‘To snap with the teeth; to squeeze or crush with a snap of the jaws or by the sudden shutting of a window, door, drawer, or the like; also to make a noise like that of snapping teeth, to clack, clatter, click. Also of the cry of a bird.’
See also ‘stitter’.
Source: Henry Williamson, Tarka the Otter: His joyful water-life and death in the two rivers, illus. C.F. Tunnicliffe (Harmondsworth: Puffin Books, 1976 (1927)), p. 57