  Complex systems having metastable elements often demonstrate nearly log-time
relaxations and a kind of aging: repeated stimuli weaken the system's
relaxational response. Granular matter is known to exhibit a wealth of such
behaviors, for which the role of thermal fluctuations is usually ignored.
However, we demonstrate that the latter can pronouncedly affect contacting
mesoscopic-scale asperities and be macroscopically observed via appropriate
acoustic effects. We also propose a mechanism comprising slow relaxations and
aging as intrinsic properties of a wide class of systems with metastable
states.
