[help] Buzzing sound

[nooktablet]

I was using ColorDict to look up some words, and suddenly the tablet became unresponsive, i waited and after about 15 seconds it rebooted, while it was rebooting, i heard the buzzing sound, looks like it's from the speaker, but not sure though. after rebooted, no more buzzing sound

The same thing happened a few hours ago when i opened google play music, play songs, put the tablet in sleep mode, after a few minutes the buzzing sound thing happened, because it was in sleep mode, i tried to wake it up by pressing the power button and nothing happened (i guess it froze), then i forced it to shutdown, but if my brain is correct it rebooted itself, i did force it to shutdown, but it did not shutdown, it rebooted itself automatically.

Also i was using text-to-speech in ColorDict, which reads the word, which means it used speaker. i'm assuming this caused the problem

when i used colordict, volume was low, the buzzing sound was not loud
when i listened to music, volume was higher, the buzzing was very loud
-> that's why i think the sound is from the speaker.

Is this a problem with Jelly Bean or does it have something to do with my creaking sound or hardware defect?

thanks