Buying my first Mac this afternoon at an Apple Store. Getting a 15" MBP, 2.8 Ghz, 4.0 Gb. I'm getting the 500 Gb traditional hard drive. $50 to upgrade to the faster hard drive doesn't sound too bad, but I've read a few threads about beeping and clicking in the faster HD's. Is this problem widespread? Is there a noticeable speed difference with this HD upgrade?