Why Ping VM-Machine lost 10% ?

I bulid a VM-machine in my windows 7 X64, use VM Workstation 7. the VM-Machine's OS is Windows server 2008 R2.

I set VM-machine 's Net to Bridged. I just worked. I mean, VM-machine can visit Internet.

I found when I ping VM-machine  from my physics PC. It always lost package some time. As a test, I send 3000 packages, and lost 337.

Why? where is the maybe problem?