Hi all, I hope you can help me.
My set-up is a macbook pro 17 inch quad core 2.4 processor and 8 gigs of ram. I use the babyface with Pro Tools 10.
When I start mixing a track, the session works easy without any issues.
But as soon as I reload the session another day, the cpu(native) metering in pro tools starts to spike heavily. With the consequence of having an output that pops/cracks. The cpu spike is from 40% to 100% on a constant base.
When I mix my playback engine is set on the highest buffer size (1024), I use 7 processors at 99%. And delay compensation set on the samples needed per session.

The curious thing is, when I playback a session using the internal macbook soundcard or a firewire soundcard, the session runs smoothly. No spikes in the cpu(native) metering. The cpu processing is very steady. Maybe it deviates from 2 to 4%
I am also using the latest firmware and driver. 
I'm also using the extra usb cable for extra power.

In theory usb 2 (480mbps) is supposed to be faster than firewire 400. Is there something I am missing here?

I hope you guys can help me.