R u giving syrups which docs normally refers for babies .. gas is normal .. just give some warm oil massage at his stomach area every before bath , if any gas struck may flush out ..
Could be comic or reflux.. if concern pls seek advises from your PD. May this information helps too: https://www.healthline.com/health/parenting/newborn-grunting#causes
Absolutely normal, my lo did the same thing too(: But if you're concerned do consult the pd.