Well since you're purchasing that WD 500 GB HDD why not consider another option? I assume you would plan to use that WD HDD in your present system. You're not planning to build or buy another system, are you?
So assuming you're going to utilize that HDD in your present system and further assuming that your old HDD currently boots and functions without any problems (other than generating some noise) do you think you might consider cloning the contents of that old HDD to your new WD HDD? That way ALL your data on the old system, including the OS, all programs/applications, configurations, personal data, etc. will be available to you. It's really a simple solution as long as you're completely satisfied with the old system as it now stands (with the exception of a possible failing HDD). The disk-cloning process is relatively simple & straightforward. If you're interested in this approach we can provide some suggestions as to a disk-cloning program (freely available on the net) and how to use it.
As to the current HDD. It would be a good idea to use a HDD diagnostic program to test the drive. That type of program is freely available on the net. If you're interested so indicate and provide the name of the manufacturer of that disk. On the other hand perhaps you're going to junk it since there's some evidence (although not conclusive) that it's failing.
I'm sure the USB external HDD you're planning to purchase will come in handy. My advice to you is to opt for a separate USB enclosure and a separate HDD rather than purchasing a commercial product containing a single-unit enclosure + HDD. Take a look at the offerings at Newegg. You'll have much greater flexibility this way and the total cost should be roughly the same. Also opt for a system that has USB 3.0 capability since it's backwards compatible with USB 2.0. So even if your present system is only USB 2.0 capable the USBEHD will work with it. And later when you get a new system with USB 3.0 capability you'll be able to use the USBEHD to get the greater speed of that protocol.