BigIP LTM is reponded ping requests for address that do not exist in our network

the f5 can respond to pings for addresses it owns (Self-IP, SNAT, virtual IP addresses). I believe that it can respond to ICMP requests for networks that are defined in its virtual address list as well. If you have any network virtual servers (IP forwarding, fast-l4, etc.), verify that those network virtual addresses have ICMP disabled. Navigate to Local Traffic | Virtual Servers | Virtual Address List, click on the network address, and verify "ICMP Echo" is disabled. keep in mind, depending on the forwarding-vs configuration, this could prevent ICMP messages from being passed through to backend networks