Latitude D600 hard drive overheating

I've just replaced the 20GB 4200rpm Hitachi Travelstar drive in my six year-old Latitude D600 with a Western Digital 160GB 5400rpm Blue Scorpio drive. It's running significantly hotter than the old drive; I can't rest my hand comfortably on the palm rest, and the variable speed exhaust fan revs up to high speed early on, and remains there. The old drive didn't really run cool, but it wasn't this hot to the touch and it didn't cause the fan to run at high speed all the time. I've downloaded a few utilities to read the SMART data from the drives; I'm getting mean operating temps of 122 - 130 degrees for the WD drive. However, I don't think this data is reliable, as when I reinstall the old drive, I get readings of 130 - 135, yet I can tell by touch that the newer drive is hotter, and by the fact that the fan is always on high.

I contacted WD's tech support; they sent me a reconditioned replacement drive, but the problem persisted, so I sent it back and kept the first drive.

Is this a known problem with this system? Was it not designed to properly ventilate larger, faster drives? The physical dimensions of the two drives are the same. I looked at the available Dell replacement drives for this system; the largest is 80GB (which would be fine), but they are 5400rpm drives.