Hello, a friend of mine asked me if I knew the song with the following line: "Where is the sound I heard before". The line is said (?) by a female voice. It should be a well known trance song (in Belgium). I can't give more specifications, 'cause I didn't hear the track myself. If anyone can help me and my friend. Thanks

The MacKenzie feat. Jessi "Without You" matches your description. Nice track, too.