Raid 0 for audio processing

I am in audio processing with Logic, and I just switched from an old MBP first gen (core duo 2.16) to a brand new MP hexa 3.33 with 16gb ram, and I have the following setup for the disks :
- boot and Logic : SSD, Optic bay
- songs : 600Gb Raid 0 for songs (Logic user folder) out of 2x1To WD, bay2&3
- samples : 400Gb from the remaining 1To, bay 2
- other : 400Gb from the remaining 1To, bay 3
- backup : original 1To Wd, bay 1

So far ok, but I experience now very frequently a delay now in Logic when I hit play / stop in a song, I have to wait that the HD makes a kind of wake up, I can hear the typical noise of the disk, and wait for Logic to restart after loading the part of the song where I am. I wonder if it is related to the raid 0 configuration may be not appropriate for this kind of intensive use (2 disks to run with heavy steraming) ?? But with my old MBP and a 500BG WD, there is no such "wake up" time, so I am perplex..
When you work on a song it's very annoying to wait 1.5 second that the disk wake up !
Any idea ? buffer size ? etc..Thanks

 

OK, I uncheck the the option to stop the activity of HD asap, I will see if it change, thanks