Gastric reflux is one of the non-motor symptoms of PD. It can cause irritation of the vocal folds and throat and can potentially cause voice hoarseness. It is possible that a person who has reflux doesn't have any symptoms of reflux that they recognize. For example, sometimes people feel as though they "have something stuck in my throat" after swallowing. These people may even seek a swallowing evaluation which turns out to be within normal limits. The reason is that when reflux irritates the vocal folds and throat area it can give the person the sensation that there is something stuck in their throat when, in fact, there is not. Another possible symptom of reflux is frequent throat clearing.
Parkinson disease itself can cause voice changes as well including soft voice, monotone voice, and hoarseness. Frequently people with PD have bowing of the vocal folds meaning that the vocal folds don't come together completely during talking. When the vocal folds do not close completely air can leak through resulting in a breathy or hoarse sounding voice. If you have reflux and vocal fold bowing the combination of these two factors can cause changes in your voice that could potentially interfere with functional communication.
If you think that you might be experiencing symptoms of reflux or changes in your voice you should consult with your physician. Successful management of reflux is usually a combination of medication and behavioral modifications. For example, it may be recommended to stop eating several hours before going to bed at night, eating more frequent smaller meals, raising the head of your bed, or making changes in your diet. A speech-language pathologist can advise you about behavioral modifications that may help you and can also advise you about receiving behavioral voice treatment to improve your communication abilities.