The ornamental design for a balloon with a sound chip, as shown and described.
FIG. 1 is a front elevational view of a balloon with a sound chip showing my new design;
FIG. 2 is a right side elevational view showing the design on a slightly larger scale than in FIG. 1, the left side view being a mirror image of the right side shown;
FIG. 3 is a bottom plan view showing the design on the same scale as in FIG. 2; and,
FIG. 4 is a rear elevational view showing the design on the same scale as in FIG. 1.