I'm new at this so if its already asked sorry to waste anyones time but:
I flushed a toilet tonight and one in another part of the house started gurgling. I've never had that happen before. We are on a septic system so I'm really hoping that it isn't a septic system problem. We've just redone the roof including replacing all the vents. I've also noticed an occasional 'sewage' smell coming from my kitchen sink. I'm hoping it's just a vent, not a septic issue. Any help would be so much appreciated.
Sounds like you have a partially blocked vent. The system has to get air for the water to flow, if the vent is clogged, it will pull it from toilets, sinks, etc. This causes toilets to gurgle, and sink traps to be sucked dry, allowing sewer gas to escape.