I currently own a 2003 Hyundai Accent GSI automatic.

since this winter, the transmission has randomly given a hard thump/knock/push mainly when I let go of the gas while driving in the city which presumably downshifts, but recently when doing so it slows the car down for a split second slightly throwing me forward. This seems to happen after cold or humidity, and the issue doesn’t persist once I’ve been driving for 10-15 minutes. No check engine codes related to it after scanning

 

Hey Seanmtl, have you had this checked out yet?? Car still running?? Has the transmission ever been fully flushed?? I'm REALLY surprised it hasn't thrown a code or CEL!