Weeping Willow Trunk Problem?

Hi. I'm George Todd from Andes, NY. 3 years ago my wife and I planted a weeping willow tree in a very wet location on our property. It seemed to thrive. However, yesterday I noticed that when I knock on the trunk about 1 1/2 feet up from the ground it sounds hollow. Root-like structures have grown away from the trunk proper about 1/2 inch although they are bark covered - loosely. There is also a thickening of the trunk in this area and then above that it returns to a perfect strong trunk about 2 inch circumference.

The tree has doubled its height each year and we love it and want to save it. Does anyone know what I am dealing with and if there is a way to save our tree that we've named Wilbur.

Thanks in advance. Sincerely, George Todd

 

without more info not much can be surmised. Any chance of some pictures of the affected areas/parts?

 

Thanks for your reply. I'll try to post some pictures in a few days. I have to borrow a digital camera. Thanks again from my wife and I, Sincerely, Joan and George