Random audio problems; different problems depending on where audio is from

Question

If I play loud music such as the Lord of the Rings or The Dark Knight soundtrack, the MBP speakers will sometimes crackle. However, if I plug in my external speakers, then the crackling will probably still occur in the same song, but at a different time. If I plug in my earphones, then there may or may not be a problem in the song again, but if so, then it will probably be at a different time in the song.
Why is the problem not consistent? Also, if my earphones crackle, does that still mean that the problem is in the MBP, or is the problem actually in the earphone? I thought that if I plugged in earphones or speakers into the MBP, then only the plugged in device would vibrate to make sound, and not the MBP, so the MBP should not crackle even if the internal speakers are busted when earphones are plugged in?

Answer 1

I was using Sennheiser earphones for a few years. They worked fine up until a month or two ago, when the buzzing began. After that, I tried out my iPod earphones for a day or two but they had the same problem. A pair of cellphone earphones also has the same problem, as well as my Creative external speakers.
The buzzing used to only be in the right ear but recently it seems like it can happen from both the left and right, although still mostly from the right.
I don't think the problem are my ears; it just doesn't sound like it's coming from inside my head, and I clear my ears regularly, anyway. Also, I asked a few other people if they can hear the sound and sure enough they could, so I guess I'm not crazy.
I almost never use the MBP internal speakers; I'm usually using my external speakers. I do occasionally play loud music, but wouldn't that just blow the external speakers and not the internal ones?