"a poltergeist is a ghost that can move solid objects that the usual ghost wouldn't normally bother with. They usually do this to get someone's attention for various reasons, like if they were mad at you for being near the spot where they died... or a place that means a lot to them (of course, all ghosts have a reason for what they do,otherwise they wouldn't be haunting in the first place)
You did have the meaning in German, "noisy ghost" thing correct. In a way, they can be noisy. It depends on what they're throwing (a pillow, compared to a brick)."