Further Plumbing Worries

Last night's glug, which I believed to be localized to the upstairs bathroom, is apparently some sort of system-wide failure. When the downstairs toilet or any drains (sinks or showers) in the house are used, the upstairs bathroom drain makes a tremendous glug glug glug. This, in my understanding of plumbing, is not good. Jake says this means that the studor vent is off the hook, since the other bathroom fixtures have a different vent. This leads us to wonder if there's something wrong with the city drainage system (we did get a ton of rain yesterday and last night) or if there's something in 83 Durant's pipes. Like a poltergeist.