Sub DelRandData()
Dim rng As Range
Dim i As Long, x As Long, y As Long

Set rng = Selection

On Error GoTo ErrHandler

Application.Calculation = xlCalculationManual
Application.ScreenUpdating = False

For i = 1 To Int(rng.Cells.Count * 0.07)
retry:
    x = WorksheetFunction.RandBetween(1, rng.Rows.Count)
    y = WorksheetFunction.RandBetween(1, rng.Columns.Count)
    If rng.Cells(x, y) <> "" Then
        rng.Cells(x, y).ClearContents
    Else
        GoTo retry
    End If
Next i

Application.Calculation = xlCalculationAutomatic
Application.ScreenUpdating = True

ErrHandler:
Application.Calculation = xlCalculationAutomatic
Application.ScreenUpdating = True

End Sub