Netstat says connection in SYN_SENT but tcpdump captures no data

EDIT: tcp_fin_timeout DOES NOT control TIME_WAIT duration, it is hardcoded at 60s

As mentioned by others, having some connections in TIME_WAIT is a normal part of the TCP connection. You can see the interval by examining /proc/sys/net/ipv4/tcp_fin_timeout:

[root@host ~]# cat /proc/sys/net/ipv4/tcp_fin_timeout
60

And change it by modifying that value:

[root@dev admin]# echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout

Or permanently by adding it to /etc/sysctl.conf

net.ipv4.tcp_fin_timeout=30

Also, if you don't use the RPC service or NFS, you can just turn it off:

/etc/init.d/nfsd stop

And turn it off completely

chkconfig nfsd off

From data you provided I'd say it's related to some NFS mounts or something using RPC.

you can check with rpcinfo -p for ports that might be used by some of RPC related services.

Here is how it looks on my system

# netstat -nlp | awk '{if ($NF == "-")print $0}'
tcp        0      0 0.0.0.0:55349           0.0.0.0:*               LISTEN      -               
udp        0      0 0.0.0.0:18049           0.0.0.0:*                           - 

# rpcinfo -p
   program vers proto   port
    100000    2   tcp    111  portmapper
    100000    2   udp    111  portmapper
    100024    1   udp  10249  status
    100024    1   tcp  10249  status
    100021    1   udp  18049  nlockmgr
    100021    3   udp  18049  nlockmgr
    100021    4   udp  18049  nlockmgr
    100021    1   tcp  55349  nlockmgr
    100021    3   tcp  55349  nlockmgr
    100021    4   tcp  55349  nlockmgr