The phrase "are noticeable only" is correct and usable in written English.
It can be used to indicate that something can be perceived or observed exclusively under certain conditions or contexts.
Example: "The changes in the design are noticeable only when viewed from a distance."
Alternatives: "can be seen only" or "are apparent only".
Nuclear forces, in contrast, are noticeable only on subatomic scales.
The pleasures of the game itself are mostly in the details — in the subtleties of pitching and bunting and baserunning, many of which are noticeable only to adepts.
The markings really are noticeable only upon close inspection — and hardly noticeable at all, the thinking goes, to a driver who is calling in his pizza order.
Some tweaks are noticeable only to obsessives, but other tweaks, equally small in terms of how many words are changed, can become legendary.
Results reveal that stiffness of the plate increases due to the viscoelastic nature of the materials and the relaxation effects are noticeable only after a remarkable number of oscillations following the impact.
The moss is microscopic for most of its existence, and plants are noticeable only after they begin to produce their reproductive structures.
Jennings' country background is noticeable only in the wailing violin, but you need to add something to a cover.
This was noticeable only during an eclipse because the Sun's brightness would otherwise obscure the affected stars.
She also stressed the possibility that sexual side effects in female cyclists might be noticeable only in longer-term studies.
But the effect of zone defenses, since they became legal in the 2001-2 season, has been noticeable only to the trained eye.
And as the Labor Party meets in this misty seaside town this week for its annual conference, Mr. Blair — the dominant force in British politics for the last decade — is noticeable only by his glaring absence.
