[VB.NET]窗体资源释放问题

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窗体资源释放问题
我在一个非系统启动窗体上用以下代码播放一段背景音乐，为什么我关闭该窗体后，背景音乐还不消失？请问怎么把音乐也去掉。
Private Sub frmHomePage_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim SoundInst As New SoundClass
SoundInst.PlaySoundFile( c:/平湖秋月.wav )
SoundInst.PlaySoundFile( )
End Sub

Public Class SoundClass
Declare Auto Function PlaySound Lib winmm.dll (ByVal name _
As String, ByVal hmod As Integer, ByVal flags As Integer) As Integer
name specifies the sound file when the SND_FILENAME flag is set.
hmod specifies an executable file handle.
hmod must be Nothing if the SND_RESOURCE flag is not set.
flags specifies which flags are set.

The PlaySound documentation lists all valid flags.
Public Const SND_SYNC = &H0 play synchronously
Public Const SND_ASYNC = &H1 play asynchronously
Public Const SND_FILENAME = &H20000 name is file name
Public Const SND_RESOURCE = &H40004 name is resource name or atom

Public Sub PlaySoundFile(ByVal filename As String)
Plays a sound from filename.
PlaySound(filename, Nothing, SND_FILENAME Or SND_ASYNC)
End Sub
End Class
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音乐没有关
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怎么关掉啊？（注：代码中SoundInst.PlaySoundFile( )是多余的，不好意思。）
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SND_SYNC
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