I think something within the hard drive is in the wrong place.
Is it safe to open the 2.5 inch hard drive? Or is there something else I can do?
"Weird" noises from hard drives are a sign of impending failure. The noise may be from the stepper motor, its bearings, or the drive heads. In all cases, unusual or excessive noise is a sign of a problem. If you can access data on the drive, copy everything you need from it immediately. If not, you have a few choices (in order of preference):
It is definitely not safe to open the hard-drive up. By doing so, you would risk letting dust in; the smallest amount of which could do even more damage to the drive. Besides, your chances for fixing the mechanical parts are very slim.
If the drive is still under warranty, try to have it serviced.
Can you still access the data on it? If so, make a full backup immediately!