This video from the USA says about itself:
29 August 2016
Cluck – Cluck or Knock – Knock on wood sounds echoing loudly through the forests and mountains – these incredible sounds are made by [Eastern] Chipmunks and seeing is believing! After three years of documenting these loud sounds that carry for 100’s of yards through the forest and suspecting they were from Chipmunks, but not knowing how they could be so loud I’ve finally caught the little ones in the act. They put a lot of effort into these calls with full body involvement.
This loud calling typically starts in late summer – here in the Great Smoky Mountains it was August 29th. These calls have absolutely nothing to do with a warning call after seeing predators such as hawks as some scientists have concluded in limited studies mostly in the northeast, but likely have everything to do with Chipmunk communication, perhaps territory. These sounds will echo through the forest sometimes for hours with several joining in especially in October. Because Chipmunks are so small and the forest so vast it is very hard to actually find the source of these loud wood-knocking noises, but today I got lucky with one sitting on a pile of rocks at the forest edge – the Chipmunk seemed to enter an almost trance-like state for a few minutes.