What Causes Boing Sound In The Ears After Swimming?

Hi, I just went swimming today. Now, I hear a boing noise in my left ear whenever I hit it. I'm thinking its water in my ear but it dosen't sound like the symtoms of the water in ear "cases" on other web pages. This also happened last summer after I went swimming also. It went away the next day. There is no pain or loss of hearing (that I can tell). I'm just wondering what the sound means....