I need help with noisy mascerator?

a grinding noise, which is progressively getting louder and longer. Its alsmost like it recycling itself, as it does this periodically and can be as much as 3 times in an hour We are also exsperiencing a flash back from the sink unit when the noise happens or when we flush the wc. Is there something that we need to pour down the wc to flush through the mascerator.