Around two weeks ago I started a local website and since then it has improved from the bottom of page 3 to #18. However, lately, I have been observing something very strange: Very regularly (now daily) the site jumps completely out of the SERPs for its main keyword. Only to return to the same (or slightly improved) position several hours later. I'd say alright - this is probably just the Google Dance. But what's really strange is that whenever my site jumps out of the SERPs, so does the site that belongs to our main competitor who has been on #1 for the last couple of months. When my site returns, so does the site of our competitor. Webmaster Tools reports no issues with my site. The only links I have built so far are around 30 entries in local directories and 3 PBN links that don't seem to have gotten indexed yet. What could be going on here?