'noteworthy exception' is correct and usable in written English.
You can use it to acknowledge that something is not true, but there is one exception. For example, "Generally speaking, cats don't like baths, but there is one noteworthy exception - my cat loves them!".
There was one noteworthy exception.
Orchidaceae rarely have fleshy fruits, but the genus Vanilla is a noteworthy exception.
One noteworthy exception was the Metric Act of 1866, which permitted use of the metric system in the United States.
One noteworthy exception came as the soprano Renee Fleming sang Mozart's "Exsultate Jubilate," when the archbishop closed his eyes and swayed for a moment, as if transported.
One noteworthy exception is the guitarist Nels Cline, who released an excellent album last year called "New Monastery: A View Into the Music of Andrew Hill" (Cryptogramophone).
Its chief characteristic was a strong monarchy in a rather rustic and backward economy (with the mining industry a noteworthy exception).
Last month's slackness in the labor market encompassed virtually all industries, with few noteworthy exceptions.
But with some noteworthy exceptions, the teachers didn't seem to be engaging the students.
Thus, with a few noteworthy exceptions, this mechanistic approach did not find its way into mainstream geomorphology until the mid-twentieth century.
With a few noteworthy exceptions, the European cinema is becoming increasingly complacent, a living museum of cultural values and national pride.
Two noteworthy exceptions to this trend were John Darnielle, who records under the name the Mountain Goats, and Craig Finn, who leads a band called the Hold Steady.
