My DD is 5 months. She does incredibly high pitched squeaks when she's playing. For weeks I have told myself this is just a happy baby learning to 'sing', but the truth is it gives me a bad headache and it goes on for hours. Is she bored? She mostly squeaks when she's playing on the mat with her toys and baby gym. She doesn't squeak when we're out in the buggy or if daddy is in the room (typical!). I mean, I think when something really holds her interest she is quiet, but I just can't be that interesting all day long!