Internal reading voices (IRVs) is a phenomenology of inner speech when a person happens to hear voices, particularly while reading the text messages and or books. These IRVs were identified as the reader's own voices, and sometimes as the voices of other people. This phenomenon may be a premise for auditory verbal hallucinations (AVHs). According to a journal article titled "Inner reading voices: An overlooked form of inner-speech: Psychosis: Vol. 8 No. 1" written by Ruvanee P. Vilhauer, IRVs may provide evidence for individual variation in imagery vividness and support for inner speech accounts of AVHs. And this is mostly due to there are many individuals report routinely experiencing IRVs, which often have the auditory qualities of overt speech, such as recognizable identity, gender, pitch, loudness and emotional tone. While some individuals reported that IRVs, both controllable and uncontrollable, were continuous with audible thoughts. Thus, these silent voices were mostly interpreted as the auditory imagination, which is akin to visual imagery, that occurred spontaneously, and maybe linked to "imaginary vividness". Therefore, hearing voices may not be linked to mental health issues. However, those who don't imagine voices in their head, due to lack of internal voices, may have linked to health issues and related to poor reading ability in those who have dyslexia, which means that those people who hear voices while reading the text messages does actually indicate that they are a good reader. Therefore, hearing voices in your head, as a phenomenon, is considered to be normal.

Source Reference:
Inner reading voices: An overlooked form of inner speech
Silent Reading of Direct versus Indirect Speech Activates Voice-selective Areas in the Auditory Cortex