[avaserfi]

If the resonant frequency is within the room REW should be able to help you find the issue, but that won't be the case with cabinet resonance. Cabinet resonance is not measurable via typical methods of measurement, but rather, in an far field anechoic situation using impulse response tones at varying angles then a waterfall plot would need be derived for cabinet resonance to show up on a plot.

A more simple method would be using an accelerometer attached to various point on the cabinet and then averaging the responses. It is however fairly likely that your speakers do have resonant cabinets as most DIY and commercial speakers have fairly resonant cabinets.