MacBook Pro experiencing ping spikes to local router
I'm posting this reply on a few threads to make it easier to find.  I chased the same issue and finally found the cause.

Locationd.  Open the console app and watch while you do a continuous ping.  Every time you see latency spike, you'll see entries for locationd.  Go to System Preferences -> Security &amp; Privacy -> Location Services.  From there, you can disable and you'll likely see the problem disappear.  However, you lose the "find my mac" ability. 

What made mine acceptable was going to system services (scroll down)->details->check show icon in menu bar when [...].  Then, take look at what is requesting location.  Disallowing Evernote helped a lot.  I pruned down to the minimum and the frequency of the spikes has gone down to an acceptable level for me.

edit: filed a bug with Apple because even when location services are disabled, locationd scans (verified in console), impacting latency. Apple marked it as a dupe, so hopefully fixed soon.