Dallin: Will you play trains with me? Here, you be the helicopter. 

Me: *makes helicopter noise*

Dallin: (looks disappointed) No mom, like this: tick tick tick tick. 

Me: chika chika chika chicka 

Dallin: chick chick chick chick

Me: ticka ticka ticka ticka 

Dallin:  toka toka toka toka

I don't think we ever agreed in what sound helicopters make.