well, I just called and the guy tried to hear it on his own kindle for a while, then eventually decided the kindle just isn't supposed to do that. I was kind of surprised, I thought they'd tell me it was normal and quit complaining but I guess they're going to send out a new one. oh well, at least I'll be able to check if the new one does it too.
I have to say Amazon is doing customer service well. I got straight through to a friendly support guy. I didn't even have to speak my order number into some voice recognition or anything.
so yeah...thanks for the input everyone.