“RSS” stands for “resident set size,” one way to measure the amount of memory used by a process in Linux. It does not refer to RSS feeds. This probably has very little to do with WordPress, and everything to do with the amount of RAM in your box and how much memory Apache is using. I would recommend looking for answers on Server Fault, ie. Apache hanging with MaxClients is reached. You may be trying to spawn more Apache children than memory allows.
