It happens with certain yeast strains. I had one that literally smelled of rotten eggs! It was like the 3rd beer I had ever brewed and my wife wasn't happy with the hobby I had picked up that night.
The beer turned out great and since then (about a year later) I haven't really experienced anything that nasty. I also use a lot of safal-05 and notty which is probably why.
Primary 1: Winter Tropics Pale Ale
Primary 2: Appy IPA
Primary 3: Truly Triple Hopped IPA
Secondary 1: Air
Secondary 2: Air
Bottled: Edworts IPA, Nierra Sevada, Stork Blue Celebration Ale
On Deck: Maroon Effect Amber, Blonde, IPA, APA