ping to Cisco 6509 MSFC router time out intermittently

Have several cisco 6509 as core switches.
ping to the router groups and access switches time out intermittently,
On the routers telnet session, the standby-6-statechange messages as the following appear intermittently.

2y12w: %STANDBY-6-STATECHANGE: Standby: 3: Vlan3 state Speak -> Standby
2y12w: %STANDBY-6-STATECHANGE: Standby: 3: Vlan3 state Standby -> Active
2y12w: %STANDBY-6-STATECHANGE: Standby: 3: Vlan3 state Active -> Speak
2y12w: %STANDBY-6-STATECHANGE: Standby: 210: Vlan210 state Speak -> Standby
2y12w: %STANDBY-6-STATECHANGE: Standby: 210: Vlan210 state Standby -> Listen
2y12w: %STANDBY-6-STATECHANGE: Standby: 3: Vlan3 state Speak -> Standby
2y12w: %STANDBY-6-STATECHANGE: Standby: 140: Vlan140 state Standby -> Active
2y12w: %STANDBY-6-STATECHANGE: Standby: 140: Vlan140 state Active -> Speak
2y12w: %STANDBY-6-STATECHANGE: Standby: 50: Vlan50 state Standby -> Active
2y12w: %STANDBY-6-STATECHANGE: Standby: 180: Vlan180 state Speak -> Standby
2y12w: %STANDBY-6-STATECHANGE: Standby: 3: Vlan3 state Standby -> Active

What could be causing the standby routers state changed continuously, and resulting the time out to switches and inter vlan hosts?

Thanks.
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Patrick GohEngineerAsked:
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JustInCaseCommented:
Cause could be anything that will prevent hello packets to be created, or to be received on other switch (including bad timers):
- HSRP timers
- losing communication between routers (high CPU usage, network loops)
- STP problem

Try Cisco's troubleshoot HSRP article.
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giltjrCommented:
Not directly related, but I would change your configuration so that you see the time when the messages were issued.  This will give you a better idea of exactly when the issues are occurring.   With your current settings all you know is what week, relative to last restart (which was 2 years and 12 weeks ago), the issue occurred.

 service timestamps debug datetime msec localtime show-timezone
 service timestamps log datetime msec localtime show-timezone
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Patrick GohEngineerAuthor Commented:
Finally found that there was a network loop on a DLink hub in vlan2. We had few incidents of network loop in the past, this is first time I saw it affected more seriously to the routers than  the switches. Thanks a lot, Predrag and giltjr.
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