Brownsburg resident that lives on the other side of town, I was curious as to what was going on.
When I got to the customer's house, I first smelled the water at the kitchen sink faucet and didn't smell anything. I filled a glass with water and still didn't smell any odor. When we went into the master bathroom however, there was a smell right away, but not from the water, at least not the day that I was there. The smell was actually coming from the drain. I removed the drain stopper and saw residue in the slots in the drain assembly. I cleaned these out with a Q-Tip, stopped up the drain with a rag and then poured liquid bleach into the drain to the point that it filled the slots in the drain assembly. I did this for both sinks and asked the customer not to use the sinks until the next morning. This did take care of the smell coming from the drain, but the smelly water came back the next day. The customer said that she was going to contact the builder to see about having them replace the faucet.
There is no definitive answer as to what is causing the sulphur smell. It could be the faucet, drain or supply tubes for the faucet. My best suggestion is to go back to the builder and see what help you can get. If the house is out of warranty, then replacing the faucet and supply tubes may be the way to go, but again, there is no guarantee that this will fix the problem long term.