The client in ISC DHCP 4.3.5 (and probably in older versions) does not 
wait between sending DHCPDECLINE (bind_lease() in client/dhclient.c) and 
sending DHCPDISCOVER (state_init() in client/dhclient.c).

If the call of script_go() in bind_lease() keeps failing (e.g. when 
somethings breaks in dhclient-script), the client will spin in a
DHCPDISCOVER-DHCPDISCOVER-DHCPDECLINE loop as quickly (and as long) as 
the server can respond.

RFC 2131 says clients should wait at least 10 seconds between DHCPDECLINE 
and DHCPDISCOVER. See page 16:

      [...] If the client detects that the address is already in use (e.g.,
      through the use of ARP), the client MUST send a DHCPDECLINE message
      to the server and restarts the configuration process.  The client
      SHOULD wait a minimum of ten seconds before restarting the
      configuration process to avoid excessive network traffic in case of
      looping.

-- 
Pavel Kankovsky aka Peak                      "Que sçay-je?"