"When an amplifier is pushed to create a signal with more power than its power supply can produce, it will amplify the signal only up to its maximum capacity, at which point the signal can be amplified no further. As the signal simply "cuts" or "clips" at the maximum capacity of the amplifier, the signal is said to be "clipping". The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a sine wave becoming a distorted square-wave-type waveform."
I think it sum up what I mean by distortion, in fact it's more "clipping" according to wikipedia.
Yes, but what does it sound like to you? Can you describe what you hear that seems off at specific times in the song?