In the last week or so, while listening to music (loud) there will suddenly be a scratching sound on top of the music, mainly coming from the surround left speaker. It does sometimes occur in more than one speaker, which makes me think it might be the receiver. I am not sure what clipping sounds like, so I am unable to decide if that is what I am hearing.
H/K AVR140 (not enough power?) CS2, M70s, M60s. PS3 160gb playing music over optical.
EDIT: Typically scratchy/crackling will occur at approx. -12db (of +10db max)
The sound will go away, sometimes within a few seconds, sometimes after I change the song or adjust the volume. My receiver was acquired through Harmon Kardon's Refurb store, so that might be something to consider as well.