It sounds like he is possibly eating some food that he isn't completely digesting .
Have the bubble sounds been there since the beginning of the diet? If they started after introducing or increasing some food (s) maybe reduce the amount or cut it out for a while or eat at a different time of day
Without knowing more details it is hard to give more specific notes, but basically you may need to adjust what and when he is eating foods . generally digestion is better in the morning and decreases as the day goes on.
Also if the gurgling is always there instead of at parts of the day that can point to what is causing problems.