HSRP Problem

[RChee]

I have two 3662 routers with four fast ethernet interfaces on each.  Each of the 3662s are running HSRP on three of their interfaces.  The three interfaces are connected to three Cat 3512 switches, such that one interface from each router connects to each switch.  

Here's my problem.  For some reason, HSRP will not work when connected to the switches.  The symptoms are:

1.  When I do a "show standby", the local router only sees the remote router intermittently.  This causes the remote side to be listed as unknown
2.  When I disconnect the router interfaces connected to a switch and replace them with a crossover cable directly connected to each router, everything works fine
3.  When I do a "debug standby", I only see the remote router's HELLO packets sporadically
4.  On each switch, only one of the router interfaces comes up.  The other constantly comes up and goes back down.  If I remove standby, both interfaces come up fine.
5.  Using a sniffer on the switch, I see the active router broadcasting HSRP hello messages every 3 seconds.  The standby router (with it's interface constantly going up and down) sends packet in short bursts every once in awhile.

I did a "clear arp-cache" on the routers and the switches, but that didn't seem to help.

Does anyone know what the problem could be?


Rob