Excel macro: Highlight auditory collisions

Sub OverlayCheck()
Dim roomcell As Range
For Each roomcell In Worksheets("Rooms").Range("A1:A18")
    Dim room As String
    room = roomcell.Text
    Dim c, nc As Range
    Set nc = Cells.Find(What:=room, LookIn:=xlValues, LookAt:=xlPart, SearchOrder:=xlByRows)
    nc.Activate
    Do
        Set c = nc
        Set nc = Cells.Find(What:=room, After:=ActiveCell, LookIn:=xlValues, LookAt:=xlPart, SearchOrder:=xlByRows)
        nc.Activate
        If nc.Row = c.Row And nc.Column <> c.Column Then
            c.Interior.Color = RGB(255, 192, 0)
            nc.Interior.Color = RGB(255, 192, 0)
        End If
    Loop While nc.Row >= c.Row
Next roomcell
End Sub