Where does the Talmud reference the pronunciation of guttural letters?
I remember coming across a quote once from the Talmud which stated that the Jews of Galilee used to neglect their ayn (or some other guttural letter). At this point I'm not even sure if it's from the Talmud.
If anyone knows something about this then be sure to share.
I can think of a few comparisons of the sound of Aleph to the sound of Ayin:
The sound of Aleph is slight, and the letter is therefore sometimes
omitted from spelling. Ex 10:21 Rashi, citing Isaiah 13:20, Gen 13:12, Gen 13:18, Job 25:05, 2 Samuel 22:40, Psalms 18:40, Psalms 30:12.
One who gives the same pronunciation to Aleph and Ayin should not lead the prayer service. Megillah 24b Rashi, Hil Tefillah 08:12; see also Radbaz, Pri Chadash; Orach Chayim 053:16 in Shulchan Aruch HaRav and 53:37 to 38 in Mishneh Berurah. The people of certain regions of the Land of Israel were in this category.
Rav and Shmu'el debate whether Eideihen of the Mishnah
should be spelled with an initial Aleph or Ayin. Avodah
Aleph-Yud-Nun sounds like Ayin-Yud-Yud-Nun. Kiddushin 4a1 #10.
See also Berachos 32a; Kiddushin 4a1 #10; Eruvin 52; Shabbos 77.
The Gemara also mentions (or alludes to) some sort of issue about R' Chiya’s pronunciation of guttural letters (the last two just in passing):
Megillah 24b2 #18
Kereisos 08a1 #11
Mo'ed Kattan 16b1 #3
On the general connection of these letters see Deut 02:23 Ramban.