Is your xenia in a low flow area? My xenia that receives a lot of flow is moved around too much to see the pulsing.
If I turn off the pump, then it pulses.
Not all xenia will pulse in everyone's tank. Nobody that I have read on this subject can definitively say why.
One fellow hobbyist once told me his xenia stopped pulsing when his nitrates went up.
I have not seen this myself, and think it may be a case of coorelation and not causation.