Clunking noise in front end and jolting forward

When I drive on a rough road or over a bump my car makes a clunking sound from the front end. Only happens at low speeds. Only happens occasionally, usually when I don't drive it for a few hours.
Also, when I let off the acceleration my car slightly jolts forward and slows down. In order to get back up to speed I have to really get into the pedal. At that point my RPM's rise then jump back down. Other than that drives great. Ive only had the car for a month and already had to replace the starter. I was originally filling up with regular 87 octane gasoline. Since last week I've been using 89 octane could that have something to do with it? Help!