Distortion of both Midi and Recorded Analog files during play back

My system started adding distortion to the play back of both recorded analog audio and Midi (computer generated notes via soft synths) tracks.  The noise only occurs during a note, not during rests.  This is true even for the analog where the Mic or instrument is still being recorded though sound is not being produced.  The recording and playback levels are out of the red.  I loaded some old finished projects that had played without any distortion and now they all play with distortion.
As a test, I exported the tracks to a standard wave file to play back thru Windows Media Player.  Despite all the distortion heard in Sonar running thru M-Audio firewire 610 (my breakout box) the exported audio was free of distortion and sounded correct.  I've played with the buffer settings without any effect on the distortion.  I unplugged everything but the breakout box, reloaded the latest patch to sonar and the latest driver for the M-Audio 610, all without mitigating the distortion. 
 
I've looked at the other posts on "crackling" noise and couldn't find an answer.
 
Has anyone else dealt with this? 
Do you thing my M-Audio 610 has gone bad?  I've had my setup for about 2 years.  This is the first distortion problem and it began quite abruptly and without my having changed anything (that I can recall) regarding the Ccomputer.  I booted up 2 days ago and there it was.
 
Computer:  HP HDX laptop, Intel core duo P8700 2.53 G
Ram: 4 G
OS: Vista 64 bit SP 2
Sonar 8.3.1
Audio: M-Audio 610 Firewire
 
Thanks for any info

The Media Player uses the onboard card.
I bought a firewire cable from the local electronics store, but when I use it in lieu of the supplied cable, Sonar doesn't even "see" the M-Audio 610.  Perhaps it's the onboard Firewire Hardware. 

Evad


My system started adding distortion to the play back of both recorded analog audio and Midi (computer generated notes via soft synths) tracks.  The noise only occurs during a note, not during rests.  This is true even for the analog where the Mic or instrument is still being recorded though sound is not being produced.  The recording and playback levels are out of the red.  I loaded some old finished projects that had played without any distortion and now they all play with distortion.
As a test, I exported the tracks to a standard wave file to play back thru Windows Media Player.  Despite all the distortion heard in Sonar running thru M-Audio firewire 610 (my breakout box) the exported audio was free of distortion and sounded correct.  I've played with the buffer settings without any effect on the distortion.  I unplugged everything but the breakout box, reloaded the latest patch to sonar and the latest driver for the M-Audio 610, all without mitigating the distortion. 
 
I've looked at the other posts on "crackling" noise and couldn't find an answer.
 
Has anyone else dealt with this? 
Do you thing my M-Audio 610 has gone bad?  I've had my setup for about 2 years.  This is the first distortion problem and it began quite abruptly and without my having changed anything (that I can recall) regarding the Ccomputer.  I booted up 2 days ago and there it was.
 
Computer:  HP HDX laptop, Intel core duo P8700 2.53 G
Ram: 4 G
OS: Vista 64 bit SP 2
Sonar 8.3.1
Audio: M-Audio 610 Firewire
 
Thanks for any info

what are your latency buffers set to?  which driver mode are you using?  this should be the first thing you look at if you're having "crackling" or popping or stuttering on your soundcard.