Maybe he does talk, we just can't hear him because he communicates on a frequency band we humans can't pick up.Pushing this theory even further, maybe he authenticates those he speaks with using a method similar to pre-shared keys in a wireless network, that is, when establishing comms with another Decepticon he gives them a temporary virtual key to his frequency band. When he wants the conversation to end he simply takes away their virtual key. Those who don't have access can only hear a scrambled signal if trying to listen in. Eh, it's fun to imagine anyway.
![]()