Seagate Barracuda drives, and especially 7200.7, 7200.8, 7200.9 and 7200.10 series have a very common problem with heads. Seagate introduced new technology in this line - special coating for the platters that was supposed to protect magnetic layer. But in fact it caused more problems than protection. Under special conditions this coating starts to flake and tiny bits of this substance stick to the head read/write elements. Reading becomes more and more unstable, the drive starts losing tracks and at some point typical symptoms or bad heads appear - clicking, knocking, sweeping sounds ... making the data inaccessible.