Your speaking voice is created when high pressured air passes from your lungs through your vocal cords ("voice box") and throat into your mouth. The air does get into your nose and sinuses as you speak and the sound resonance from these areas helps shape the quality of your voice.
Hence, if your nose is blocked or congested, you may have a "hyponasal" or "nasal" speech. This is due to the sound of your voice not getting enough resonance from the nose and sinuses. Common causes of a hyponasal voice include:
- Nasal allergies (Sensitive nose or allergic rhinitis)
- Deviated nasal septum (a bent/crooked wall that separates the right nose from the left nose)
- Swollen turbinates (sausage-like bony structures in the nose that warms and humidifies the air that you breathe in)
- Sinusitis (Sinus infection)
- Nasal polyps
- Large adenoids (immune glands located at the back of your nose)
I would suggest that you visit an ENT Specialist for an assessment. It is quite likely that a nasoendoscopy (a relatively painless scope through the nose) will be performed by your ENT Specialist in the clinic.
Hope this helps and all the best!