distortion? audio encode?

[STARSCREAM]

Just wondering what distortion sounds like as I might have a problem and also what potential causes there are for it?
Now I may just be getting what I think is some distortion but it's in the audio track and not to do with my speakers or wiring or receiver. I've noticed when watching blu-ray's lately that sometimes when people are talking loudly (mainly in center channel) that there is some type of what I'd call distortion coming out as well as the talking. This also happens on some movies on the surrounds with airplanes flying over but I think it's how its supposed to sound maybe on those.
Could be in the audio track though because I read somebody had the same thing and named the part in transformers bd where barricade was asking sam if he was ebay username ladiesman so I went to that scene and heard it as well. One example of the planes flyover I'm talking about is on Indiana Jones KOTCS when the plane takes off from the airport and flys straight over you.