Big problem with right speaker, please help!

Ok, so i bought my first Macintosh exactly one week ago, a MacBook Pro, 15" 2.16 Ghz. I was walking on sunshine for the first days.
Then two days ago, me and my cousin were playing around with the speech controls, with the "tell me a joke" control, and suddently there is this horrible horrible screeching sound on the right speaker, it was like TV static, it was like when you are recieving bad FM transmition from your radio, and it kept getting louder. I shut down then restarted the computer, the minute the computer restarted the screeching TV/Radio static-like sound started again, then 5 seconds later it stopped and I could listen to music perfectly for the rest of the day. That was 2 days ago, the next day (yesterday) I was out the whole day so I didn't even open my macbook. Today, when I opened it, I opened itunes so I could listen to music while I was working. The music starts playing, 10 seconds into the music the right speaker stops working (no screeching sounds this time. It just stopped working: no sound at all). Drove all the way to the store, opened itunes, sound was perfect, they wouldn't exchange the computer, they said they needed proof that the sound wasn't working, they told me to go home and when sound stops working again to go back to the store. I'm back home now and the sound is perfect. I don't know what to do, even though its sounding great now there is clearly something wrong with the speaker or I wouldn't have had those problems. Even if it stops working again, it will probably start working again when I get back to the store so they won't exchange it anyway. Has this happened to anyone? I don't know what to do. I absolutely love my macbook pro, but I just paid 2600 dollars for a computer that has a right speaker problem and they won't exchange it for a new one because i can't prove it. I'm desperate here...can anyone please tell me if you had the same problem and if so how did you fix it?

That's a tough situation. It's very similar to having a car under warranty that has an intermittent problem and the dealer wants to replicate it before they'll take action. In those situations, you just have to stand firm and request that they repair it. On the MacBook Pro, I believe the speakers are integrated into the Palm Rest. I would ask that the Palm Rest be replaced or at least that they open the machine to ensure that the cables are well secured to the system board.

Other than that, I don't know how else to advise you. You may need to escalate to either store management or contact AppleCare directly. It is highly unlikely that they will replace the entire machine, so I wouldn't insist on that.