Say what? Last I checked, unless (and maybe even if) you have "wake on network administrative access" checked in Energy Saver, the Mac physically powers down the Ethernet chip and any wireless cards in it to save power.
And even if they were awake, there's no processor sending them commands, so I don't see how they could be sending anything intentionally
So I don't see how the Mac could possibly be doing what you're describing. I suppose it's possible a hardware failure of some sort is causing the network hardware (you didn't say whether it was wired or wireless) to just dump noise onto the network on its own, or when the computer tries to power it down. You could probably test this by turning that interface off in the Network prefpane--doing that should cut power to it completely, mimicing a sleep state.
Otherwise, I'd say it's MUCH more likely that you're misinterpreting the source of the network packets--maybe something else is masquerading as your MBP?