The ornamental design for a side dischargemuffler, as shown and described.
FIG. 1 is a perspective view of a side discharge muffler showing my new design and with a mounting bracket shown in phantom line;
FIG. 2 is a top view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a back view thereof; and,
FIG. 7 is a front view thereof.
The broken line showing in FIGS. 1 through 3 and 5 through 7 is included for the purpose of illustrating environment and forms no part of the claimed design.