Power Connect and Link Aggregation using cisco Catalyst 3750 doubt

Dear All

I have three powerconnect 5448 conected using LAG-LACP to a Catalyst 3750 stack (2 , 3750 switchs) , on every switch i used teh same ports :g47 and g48 and put them on a port-channel , so port g47 was connected to one switch and port g48 to the other. these three switchs connect servers, on the same segment, and catalyst do all the routing work,

I have enabled spanning tree on all of them, is necessary that ? because i have some lost packet when my Nagios Monitoring do a ping to administration interface of DELL servers and i think that some loop could be exist

i have no experience with dell switches, and copy a configuration used for link aggragation with servers and on that configuration spanning tree is enabled and load balance too