[c-nsp] FE switchport output drops

[Ras]

I've got a 4506 with a WS-X4148-RJ in it. One of these FE ports
connects back to a router (Juniper M7i in this particular case).

The port is experiencing an enormous amount of output drops (around
200pps) even though the average traffic (load-interval 30) is only
hovering around 15-20Mbps/4kpps.

I've tried SPANing the port to a sniffer on a gig port (to avoid
packets getting nuked on the drop..) over a couple of minutes (during
which the output drops increased significantly) but can't even find
any micro-spikes that would explain this.

Does anyone know what good next steps are to troubleshooting this? I'm
looking to move some traffic off the link as a preventative measure
(this is causing TCP havoc) which might help mitigate the problem but
I just can't for the life of me figure out why I'm seeing so many
drops with such a low traffic load and no visible micro-spikes.

I've had a look at the Cisco troubleshooting guide
(http://www.cisco.com/en/US/customer/products/hw/routers/ps133/products_tech_note09186a0080094791.shtml)
but that hasn't been an awful lot of help.

Thanks,
Ras