Ping Pong noise...
Thanks
Steve.
"I had this same noise when the computer was running hot. I did a reinstall of the OS, and the noise recurred. This went on for a month or so, while DW and the command line showed some disk errors, all of which were repairable so I wasn't overly concerned. But the noise infrequently continued, and the computer occasionally had difficulty waking from sleep, requiring a forced Restart using the power button. The computer finally had the HD poo-poo out (System Folder icon with prohibition sign), no amount of command line or Disk Warrior work could reclaim it. Luckily, I had a (fairly) recent back up of data; only a week or so of computing was lost (not a big deal at the time). The HD was replaced (under AppleCare). I believe the heads were the cause of the noise, perhaps they were unable to unpark, hence the clicking noise. Since this is my prime computing season, if I heard that noise today, I would back up immediately and have the HD replaced forthwith, or perhaps fivethwith."
Ping Pong noise...