I opened a store bought can ("tin") of diced tomatoes with a "pull top" lid, and unusually as I did I heard a noticeable popping noise. The lid appears to have bent inward slightly, like there was a negative pressure differential (pressure inside the can less than outside).
There is no unusual smell (although a couple of the pieces are a bit off color yellow which isn't necessarily unusual) and I know the normal issue is when there is a build-up of pressure inside something canned. At the same time this is a rather odd occurrence, and I'm wondering if it's safe to eat and if so what harmless thing could have caused this.