The bug

If you use a command to equip an item to a spectator's hands, other players can hear a noise, despite the fact spectators essentially aren't supposed to exist, let alone make noises.

It also happens for other game modes, but I'd assume it's intended to happen to non-spectators.
So yeah, if there's a command block constantly modifying a spectator's hand, it'll make really loud noises, and so I think this is a pretty bad bug.