The Bach, writing on the Tur OC 5:1, says that when pronouncing the tetragrammaton (שם הויה) as the שם אדנות, some people say the first vowel as a patach and some as tending toward tseirei. His words:
מקצתם קורים בפתח ומקצתם קורין נוטה לצירי וכן הוא מנהג האשכנזים
Other commentators discuss the distinction between a patach and a shva, and many talk about using chataf patach, however I have not seen any other discussion of this "tending toward tseirei" besides those who quote the Bach.
Does the Bach mean tseirei the same way we do? (From the Be'er Heiteiv, who quotes the Bach, and from the discussion of the Be'er Heiteiv in siman 6 seif katan 2, it would seem that he at least understands the Bach to mean a tseirei the same way we do.)
Does this pronunciation persist today? The Bach says that the "tending toward tseirei" pronunciation is the common minhag of Ashkenaz, so one would expect that it does survive.