I've been in a number of shuls where the Rov of the shul will get up before Krias HaTorah on Shabbos and say some sort of "drasha". Sometimes it was connected to the parsha or inyunei d'yoma (i.e. before a yom tov, etc.) Or sometimes to "strengthen" the kehillah with words of "chizzuk" or mussar.
Where does this come from that the Rov should speak at this time? Perhaps it was only because of convenience that usually everyone was together and also it's not disrupting a particular part of the tefillah.
Many often find this bothersome that they are being forced to listen to a drasha at such a time and rather not make the tefillah any longer than it already is.
I'm asking to see if there is any source for this "minhag" in earlier seforim or sources.
An additional point, I once heard that it says one shouldn't speak before Krias HaTorah as it's not kavod for the Torah to speak (even Divrei Torah) right before the Torah itself is supposed to be read from. Is there a makor to this?