The basic form of this onomatopoeia is . Many people would say exactly that it's the metallic noise a giant robot makes when it walks or moves its joints. Others may say it's the noise of a half-broken washing machine, or the trunk of an old car being closed violently.
You can hear many audio clips tagged with here: <
refers to almost the same type of sound, but for some reason I feel is more commonly associated with giant robots.