You'll need to check for possible real causes. For example, does the ringing a have a defined frequency ? Does your small signal stability analysis stretch far enough to capture that frequency ?
It also depends on your circuit type and where/when the ringing occurs as to whether the judgement can be made to discount it. For example ringing on a digital level after switching isn't something you might care about unless it grows.

To verify whether it is Trapezoidal ringing, there is one thing one can check.  One can plot the waveform in "point" style. The waveform needs to look like :
 *    *
*   *    *
i.e. up and down and no point in between. This is numerical artifact.

Since the waveform looks "smooth", maybe it is not Trap ringing.

Gear2 method has numerical damping while Trap method has no numerical damping. Gear2 may dampen small oscillation even if it is real.

Baolin Yang
Gemini Design Technology, Inc.