I asked him what he could hear. He was a little confused!
So I explained to him that his heart is calling to Allah and that is it's language. When he listened more carefully, he said he could hear the heart saying Allah Allah Allah Allah Allah on each beat :)
He goes round telling people that his heart says Allah Allah and sometimes puts his ears to the the heart of others and listens to see if their heart is doing the same.
My reason and idea behind this was to instil the love and fear of Allah into him and inshaAllah it'll be a lesson worth giving.
If he is naughty, I will ask him to tell me the truth. Sometimes he will clear his forehead and tell me to see if it says "liar" on it (it was not a very good way to get him to understand not to tell fibs, but it worked) and sometimes, he will say, "Listen to my heart" :)
He has understood that his heart will be good and say Allah Allah if he is also good, otherwise he fears what his heart will say.