I actually think he's clean and he's just having some crazy year where everything is working for him. His average has already started to slide over the past month, so he'll start coming back down to earth as far as BA goes. And his strikeouts are still very high as you'd expect. He's just hitting the crap out of the ball when he does make contact. And it doesn't hurt where he plays. Cambden and at least 3 of the other 4 AL East stadiums are pretty homerun friendly, especially for a power lefty bat. He has well over 100 games in those 4 ballparks. Robbie Cano has had the same fortune over his career. Same with Papi. Davis has naturally tremendous power, and he's in a good situation and on a team and in a home ballpark that really helps. I just think it's one of those years for the guy, and perhaps the type of season he'll never come close to again in his career.
But to suggest there are no advanced stats that suggest something funky is going on is ridiculous. Pretty much everything about his stats suggest something su ious. 200 points higher slugging percentage than his career average. Nearly 300 points higher OPS than his career average. The homerun rate nearly doubling his career average. As of the all stra break, he's hitting a HR every 9.3 ABs. The only guys in the history of baseball to have a better homerun rate for a season are Babe Ruth, Jim Thome, and accused and/or alleged dopers Bonds, McGwire, and Sosa. His homerun per fly ball ratio about 2/3 higher than his career average (but that is what I pointed to when I talked about the ballparks in the AL East). But more interesting than those numbers is that his BABIP and line drive rate are right in line with the rest of his career, which suggests he's not just getting lucky. It's not like he's getting way more lucky bounces or he's hitting way more line drives fielders can't get to. It's not luck. If it's not luck based on what he's done in his career, it looks even more su ious.
So even though I personally have a hunch that he's clean, there's no way you can look at his numbers (standard or advanced) and say there doesn't at least "appear" to be something fishy going on.