As per Answer ID 1704
We can only guarantee drive capacity. We cannot guarantee a particular internal hard drive model, data interface, rotational speed, or cache size in the external hard drive enclosure.
Dismantling any single-drive external enclosure to obtain this information will void the warranty of the hard drive."
Translation: “We commodity source the drives inside our external enclosures. In other words we put the cheapest possible drive on the market that we can find at any given time. It might be noisier or slower than the drive we used last month, but it’s a cost savings to us so you’ll just have to deal with it. And if you’re curious to see what you’ve purchased, we’ll void your warranty. You can buy two drives under the same model number and one may be faster than the other.”