<human>: Can you give me the gist of the text in a nutshell?

So the last couple months my big pup, a 6 year GSD, has developed notorious farts. They're often, loud, and rank. I'm not talking normal dog smell, but more "I'm not sure, he might have just pooped" kind of deals. Started doing a little research, and I'm wondering if he's developed an intolerance to whatever grain is in his kibble, as this is a common symptom. 

He's on Purina, and has never shown any diarrhea or stomach problems in the past. It's just the farts, and just the last couple months. My vet hasn't been worried about them, but I haven't yet brought up a grain-free diet with her. I'm thinking of trying a brand, and seeing if he doesn't improve on it. 

What do you guys use? What should I steer clear from?
<bot>: My dog has really rank farts, I'm looking to switch to a grain-free diet to help curb this.