The heads touching the disc won't be damaging by itself, the problem comes when a shock occurs during a read/write operation (granted, this is potentially damaging regardless whether the heads are touching or not, but the chances are greater if the heads are touching).
The psu won't cause this; it lies solely in the construction of the drive.
Though true that several HDDs probably make this noise on a regular basis, it usually isn't noticeable over the ambient noise of the case/cpu fans.
Ultimately, its up to you; were I you, and this drive were still under warranty, I would consider RMAing it.
Um, no offense but this is just not accurate. The heads of modern hard drives are positioned micrometers above the platters buffered by a cusion of air sustained by the high speed rotation of the spindle.
The heads should never actually make contact with the platters, if they make contact due to vibration or shock, they will cause physical damage to the magnetic substrate and destroy the dat on the sectors there and any sectors the debris landed on.
If you actually hear the sound of the heads scraping even for a cfraction of a second, that means that the heads cause rotational scoring and have destroyed the media forever.
However, the noise you're describing(donwload links are deleted) is probably the mechanical interface moving the head rack not physical damage. This is normal on some older drives, but on modern drives it's unusual durring normal operations.