I've had this problem plaguing me for ages. Been to Apple who at first didn't fix it, spoke to the people on the end of the phone and i'd previously looked and a power management log and saw that it was searching for a wifi signal every 30 secs or so - this is with because our wifi dropped off or someone turned it off.. Made a keyboard shortcut through automator to turn the wifi on off with some command lines i found
Re: How to create shortcut to turn on/off Wifi in Snow Leopard
The command lines need to be as follows for Ei Capitan:
if [[ `networksetup -getairportpower en1` == *On ]]
then
networksetup -setairportpower en1 off
else
networksetup -setairportpower en1 on
fi
NOTE: en1 referes to your wifi device, you will need to check what your wifi is, mine was en0.
Turn wifi off before sleeping your mac. Just started this, will be looking at if there is a better way to solve this.
Adam