Can't figure out weird noise

Mazda 3
i've got a 2012 Mazda 3 Skyactiv that's never had any sort of problems but has recently started making a strange noise. it's kind of hard to explain, but essentially what happens is any slight change in momentum results in a little popping noise that sounds like it's coming from underneath the car. for example if i launch fairly quickly, or more noticeably every time i let off the gas to switch gears there will always be a little pop the second my foot is off the pedal. also when holding a steady speed that sound will be continuous, it sounds a bit like driving over a row of little bumps.

should also note the car runs and drives perfect like it always has; just don't like hearing un-diagnosed noises.

2014 Mazda3 S GT auto, 2008 MX5 6-speed
That may be an exhaust leak. Letting off the gas pedal would cause a popping noise if there is either a high-flow exhaust muffler or a leak within the exhaust routing.
@ryandwall, I have 2012 Mazda 3 Skyactiv, 58000 miles. It works great. One thing: weird continuous scratching noise every time I am letting gas pedal off - only when car is driving. It is going on for a year and nobody can figure it out.

Did you figure out yours?