One of mine is like this each spring and late summer. this matches when the sugar levels are highest in grass. Outside of this period he is back to normal. Vets advice is good, but if possible, try feeding them earlier than usual, or smaller meals more often. I looked into it, and have heard mention of grass eating causing excess stomach acid production. on an empty stomach this can lead to the grumbling sounds and discomfort., that causes the dog to search for grass to try and settle that discomfort. vicious circle! Antacids and regular/more appropriate feeding help break that cycle.
Goo