The ornamental design for an expanding wallchannel, as shown and described.
FIG. 1 is a front, top perspective drawing of one embodiment of an expanding wall channel showing our new design, the channel in an unexpanded configuration;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is front view thereof;
FIG. 7 is a back plan view thereof;
FIG. 8 is a front, top perspective view of thereof with the channel in an expanded configuration;
FIG. 9 is a top view of a second embodiment thereof; and,
FIG. 10 is a top view of a third embodiment thereof.