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It is very possible that your rabbit has an upper respiratory infection. If caught early often all you'll see is mild discharge and gurgling. As the infection progresses then it will include bubbling of the nose, sneezing etc. The other possibility is that your rabbit is having trouble with it's teeth. Not the ones in front but the molars in the back. If there are teeth problems then you can get gurgling sounds along with the excessive drooling that accompanies this issue. BotXXXXX XXXXXne is I'd have him examined by your vet ASAP. If it is an infection it is likely it can be cleared by the next show. If it's teeth they can be trimmed and the drooling will stop.
I hope this helps, best wishes.