Well yes, you should periodically check and regrease your headset bearing cartridges. I check mine about once a year, or when I do something bad like fall in a river. However, the only.time I've personally experienced what you've described was when I reassembled my headset incorrectly. Keep in mind that if the stem was clamped down after the headset bolt was overtightened, it wouldn't be enough just to loosen the bolt. Did you also loosen the stem bolts after you loosened the headset? If you did and the issue is still there, I'd pull it apart and carefully check the bearings and races for excessive wear and lack of lubrication.