I may have missed a small Google update, unconfirmed update, that happened on June 27th/28th and there may have been an update this weekend on July 5th.
There is not a lot of chatter around it but there seems to be enough. It might be related to manual actions, but many say they do not have manual actions in Google Webmaster Tools. I doubt it was a big algorithm change because the chatter is not that high on either day. July 5th chatter may be specific to the July 4th weekend and less internet traffic happening. But June 27th/28th might be a link penalty or something else. I am unsure.
The tracking tools mostly show activity on the July 5th but very little on June 28th. Here are the charts from Mozcast, SERP Metrics, SERPs.com and Algoroo:
Did you notice any updates on June 28th and/or July 5th?