Hmmm... I'm not too sure on this one Jess... but I do know that is is very common for newborn to make lots of snuffling and grunting noises. We used to call Aidyn 'Snuffleufagus'!
If Aidan is not crying or doesnt seem bothered by it then I wouldnt be too worried, but maybe you should ask your Dr/CHN at your next visit just for some peace of mind.