Usually a 2.5 drive doesn't operate at high RPM and doesn't produce a lot of vibration. On the other hand I once bought the same external drive twice and one of them was much noisier than the other. You'll always see some variations even between the same drives. You'll have to make sure that you don't put the drive over a metal surface or something else that amplifies the vibrations.
Now if you want to be safe you should monitor your drive regularly (especially if it's new), with the wd software that came with it. Run the extended test one. It may take a lot of time to complete, but if your drive passes that test it's fine. Usually a failing drive isn't able to complete this test or breaks down during the test. You could also download...