[JohnM]

Looks like you actually have 3 resonances in that region. As mentioned in the other thread, dealing with a large resonance often unveils smaller ones that it was masking. The 120Hz feature looks to be another resonance, but one for which your measuring position is at a null - hence the sharp notch at 120Hz in the frequency response. When your main response has died away that 120Hz resonance is still going but has no contribution from your speaker output left to cancel with so its own output becomes visible.

Note that there is still a hint of the 37Hz resonance around slice 7 or 8 or so, which suggests the bandwidth of the 37Hz filter might benefit from a small tweak (checking the frequency of those little peaks will also tell you whether your filter is at the optimum frequency). Bear in mind that if you put in filters to address the resonances either side of the 37Hz peak the correction needed for the 37Hz peak will be smaller (and closer to what that mode is actually contributing). The 37Hz filter is working very well though, you would need really huge acoustic devices to deal with that passively. Absorption would help a lot for the response from about 100Hz up though.