My sourdough starter smells buttery, is this ok, or should I start over with my starter?  I have made the starter with organic whole wheat flour and water.  It is approximately 3 weeks old and I’ve made several batches of bread.  It is just starting to have a buttery smell.  Don’t know if the starter has been contaminated with another bacteria or if this might be normal. 
Starters (particularly young ones) tend to go through lots of phases while various microorganisms take root and get in balance with each other.  Changes in your kitchen environment (objects/surfaces the starter might be exposed to, along with things like changes in temperature and humidity) might affect the balance temporarily or permanently.  I'd just keep feeding the starter regularly and baking with it.  If it's still rising well itself and still allows bread dough to rise in a reasonable amount of time, the details will gradually come into balance and work themselves out.  The smell of a starter can vary considerably, from "yeasty" or "alcoholic" to "sour" and "pungent," with a lot of other possible notes like "earthy" or even "fruity."  I don't recall ever thinking a starter smelled like "butter," but perhaps you're sensing the output of lactic acid bacteria that are usually common in starters (as butter can be made from cultured cream that may also contain lactic acid bacteria).  The major warning signs that a starter has truly gone off are mold or significant discoloration, a putrid smell that won't go away even after multiple feedings, or bread that tastes/smells off in multiple batches.  Even then, most starters are probably recoverable with aggressive feeding strategies (and removal of any contamination), but those are the few times I might worry or consider getting rid of the starter. 