You already got an answer, but I'll give you an alternative, a more universal method. Please see my past answer:
How to find my programs directory[
^].
Please read my explanation on why you want to prefer this way.
Now, you could totally get rid of the file location problems and dealing with files themselves if you used embedded resources via .resx resource node. You should better used "Add Existing File" for adding the resource, In this case, the file is added to the project (as a file and its reference to the project file) and the reference in the resource file; and auto-generated C# is created, with the ready-to-use static property. If the type of your resource is not known to the system, the array of byte type will be used, which you can use for reading the resource form a memory stream. It would work great, but if, of course, your audio files are not too big.
—SA