What started out as my pessimistic irk, turned out out for the better but wasn't cheap. The wife's 2008 Equinox with only 85,000 miles was producing a faint slapping noise that could be felt by our feet. It ended up being the frame mount on the drivers side where the engine cradle attaches. It was rotted and barely holding together causing the slapping noise. I took it to a restoration/frame shop and had it repaired properly with much thicker and stronger american steel opposed to the junk metal being used by GM. The rest of the frame is in great condition.
So a warning to any one out there with a 2007 to 2014 Equinox as I was told, inspect that area on your vehicle especially if you can feel or hear any noises under your feet. I would imagine that it's not just the Equinox model effected by this.