mine, too, makes a more or less regular "parasite/spasm" noise in addition to the "normal" operating noise. I hesitated to send it back under warranty, but afterwards I kept it like that (it's in the cellar... not a disturbing noise), and for the moment it's still working "normally" with these noises.

I've got lots of others in the same series, but up to 10-14 Tb, they don't make the same noise at all.