F5 is sending via correct IP with an incorrect MAC address

Is this a BIG-IP HA pair with MAC masquerade configured under the traffic group?

If so, then you should see:

SRC IP:  x.x.x.60 (Floating Self IP)
SRC MAC: MAC Masquerade Address (use "list cm traffic-group mac" on the CLI to verify

If you do *NOT* have MAC masquerade configured under the traffic group then you should see:

SRC IP:  x.x.x.60 (Floating Self IP)
SRC MAC: xx:xx:xx:xx:5e:0b (ACTIVE unit's MAC address)

Also check that you are not mixing up health monitor traffic with user traffic in your packet capture. Health monitor traffic will be sent from both units periodically from their local non-floating self IPs and their own egress interface MAC addresses.