New HDD problem

I recently upgraded the 60GB hard drive in my original PS3 to a WD Scorpio 500GB 2.5 SATA. I went through all the steps in the guide, and have it working now. However, I have noticed that there are frequent 1-3 second lags occurring during gameplay. Blu-Rays and dvds work fine, but while playing any ps3 disks it is frequently freezing.

Any idea what would cause this or how to fix it?

Thank you!