Aircraft ground run-ups are routine aircraft engine maintenance tests which require the operation of an engine at high power for extended periods of time generating continuous elevated noise levels. The Ground Run-Up Enclosure (GRE), sometimes referred to as a "Hush House," is a structure that uses acoustical dampening principles to reduce the noise impacts of aircraft engine ground run-ups.

The purpose of the newly completed GRE at O'Hare is to minimize noise generated from all aircraft engine test runs during maintenance and repair procedures, and to reduce the number of communities impacted by aircraft ground run-up noise. The GRE is located on the scenic hold pad, adjacent to the airline maintenance area, and is oriented to direct aircraft noise toward the center of the Airport and terminal core.