Doubt has no worth only that gas invalidate the wudhu which Passing from the rear. If one hears the sound from stomach or intestine it does not invalidate the wudhu.
Please pay attention before the prayer that really it is gas or doubt. Once it is confirmed that it is not gas then wudhu is correct and in order. If it is gas then yes wudhu is batil. But again I’m saying do no give importance to doubts.