by ICMP, i assume you mean ping responses, from outside to inside?
policy-map global_policy
class inspection_default
inspect icmp
if you actually meant all icmp traffic being allowed out - they are allowed out by default, it's the return that messes with you.
to allow ALL icmp code types back in:
access-list OUTSIDE_IN permit icmp any any
access-group OUTSIDE_IN in interface outside
this explains it more thoroughly
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a0080094e8a.shtml