CPU overload MBP

HI
desesperatly need some help here.

Everyting run smoothly for 2/3 minutes with a CPU load around 45/50%, then suddenly the CPU load get to 95 % and more, the tracks are slowing down, the sound is awfull with crackles and drop etc. When i turned key Off on every tracks, all get better but CPU load remains at 75% at least, plus the overload happens again with Key OFF after again 2/3 minutes.
The CPU temperature remains stable ( same before and after the overload ).
I have a macbook pro(1.1) core duo 2g, with 2G ram, running Mac Osx 10.6.4.

I'm playing 4 FLAC analysed tracks, key ON, no other app running, tracks are on the internal hard drive HFS formated, the option 'stop hard drive ' in energy saving preference is not activated.

made some research and deleted 64bit core app with monolingual and repaired system disk authorisations from the mac osx install dvd with disk utility.
Things got normal again, but just for a day.....

All this have started after i changed my internal hard drive for a Fujitsu MJA2500BH 500G and made a clean new install of snow leopard and my apps.

really need some help, because in this state i just can't play live....

 

Could it be the FLACs? As an experiment have you tried playing on MP3s or WAVs? Just to see if you can further isolate the problem.

 

the FLAC files are good, i was playing them before my hard drive change, and yes i've tried with wave , MP3's ...the problem remains