Apparently, this one bugged me before and then it just disappeared. Now it's back and the logs get filled again with:

Aug 30 01:54:08 bogon rpc.statd[3423]: recv_rply: can't decode RPC message!
Aug 30 01:54:39 bogon rpc.statd[3423]: recv_rply: can't decode RPC message!
Aug 30 01:55:10 bogon rpc.statd[3423]: recv_rply: can't decode RPC message!
Aug 30 01:55:41 bogon rpc.statd[3423]: recv_rply: can't decode RPC message!
Aug 30 01:56:12 bogon rpc.statd[3423]: recv_rply: can't decode RPC message!

Again, not really flooding, but still annoying. While I still fail to see *which* message cannot be decoded, CentOS found a cure for this one. From looking at the diff, it seems rpc.statd is started too early (perhaps before the portmapper?). Well, restarting rpc.statd was enough to stop these messages for now - let's see if they show up again after the next reboot...