Did I miss somehting?

[BRX]

In follow freeman, if you talk to one of your female squad-followers, one of her lines is "I can't get this tune outta my head... (>>whistles<<)". What is that tune she's whistling?
Am I missing some kind of an inside-joke here? maybe it's from the soundtrack of HL1?

 

[AJ Rimmer]

I was thinking, maybe it's some obscure pop culture reference I don't get? Or just a generic tune made up by some VALVe employee with three minutes to spare?