Cisco switch CPU overload

I've a core switch (cisco 5505) with 10+ VLANs configured on that and a
cisco 7204 directly connected to it. 7204 then connects to my upstream and
we run BGP. we announce two different /21 blocks and was fine until last

We got new /20 IP block and we advertised it (added to 7204 config).
Everything is working fine but since than we see CPU overload from time to
time on 5505. The following further explains the physical connection.

    >-----------| |-----------|
Internal | |-----------| |-------->Upstream
  <-----|5505 | |7204 |
    >-----------| |-----------|

We have Rip (ver 2) running on 5505 but not on 7204. (Those two are not
talking any routing protocols each other.)
I can't figure out the reason but want urgently get this resolved. You may
contact me off list too for further info necessary.

Thanks in advance,

Priyantha Pushpa Kumara
Wightman Internet Ltd.