Ok, Just opened up and replaced my ageing 80GB HDD with a 250GB jobbie and I noticed that whilst the new drive slotted straight in, the old one had a plastic barrier fixed to it that covered up all but the SATA & Power connection plug sockets. I just wondered if this additional part on the original HDD was used to keep the airflow in check, so it can easily flow out of the vent. I tried to see if I could retro fit this 'shielding' but it was embedded onto the PCB and I would have to strip down both the original and the new HDD to attempt to fit this. In the interim I simply swapped the drives as normal, but if it is advised that I retro fit this part I will open up the case and do the necessary. This has not been referred to in any of the resources online I have found so far and I bear in mind that the Mac Mini has specific shielding that needs to be retrofitted for such an upgrade. So, it's not worth worrying about ??