Like other said. Clicking noise , means your HD is about to quit. It may be a sudden death or a slower one, with locking and corrupt recordings. If you have more than 1 receiver and pay the multi receiver fee, like Garry said thy will replace your receiver with a refurbished one. Some 630 have more problems than others, so it's a risk you may get a problematic one remember it's refurbished so somebody send it back, and I don't trust their refurbishing process, you may start having other intermittent problems. If you are contemplating replacing anyway the internal HD with a bigger one get a 1TB one (look for WD AV series). You need a special head "security" screw driver head, get it first, don't try to open the unit with standard ones. Once opened is easy to replace the HD.
Also, your unit will not work without an internal or a dead HD, you can not have only the external one.