What you are seeing is likely a response to sexual pheromones left by the females when they urinate in the common dog walking area. This time of year many dogs are in season so it could be there is one near you. Male dogs commonly lick the grass where females have urinated when they are in heat as it gives them a stronger 'flavor' of the pheromones. The tooth chattering behavior goes along with that. It may be part of 'tasting' the odor of the pheromones left in the female dog's urine.
I see this in my male dogs whenever my females are in heat. Even the neutered males will do this sometimes.
Hope this helps you!
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