Four year old regurgitating

[rowingboat]

Hi everyone,
I thought I would post to find out whether this is common or 'just us'.
My four year old has started to regurgitate food - just a mouthful. He kind of munches and swallows again.
Needless to say this is horrible to watch for me, but I am not sure whether he is doing it because he can, or because he has some kind gastric problem.
I have asked him why he does it and he tells me he can't help it, but it has had quite a sudden onset - over a few weeks.
I am planning to take him to the GP next week to check it out, but wondered if this was common amongst young children.
Thank you