I drop tune to A all the time, never had any issues with farting at all and my setup has stayed the same too.
I had this problem too. You may be over bowing and actually pulling the string out of tune. Dont push so hard into the string.Tunning my bass...(back then) piccicato and tuning it with the bow, notes had a big deflection... of course I am talking for open strings and of course I was asking if this has to do something with my crappy company made edb and its amp that I had back then... Simple question for those who know and understand. And for the up coming comments yes... I don't even have a bass right now. That kind of art its still a comfort from the money perspective... not just for me for millions around the earth...