Sonic grenade

From Halopedia, the Halo wiki

These non-leathal grenades are favored by Drill Instructors in teaching recruits to take thier time and keep thier eyes peeled. Several of these grenades were used my Colonel James Ackerson in testing the MJOLNIR-Mark V armor on Reach, hidden amongst the Pillars of Loki and used in conjuction with Naplam grenades.

References

Fall of Reach Page 262