Short Answer, Slider and pickwhip.
Since your Frequency and Amplitude are equal (30,30), put a slider on your layer (Effect>Expression Control>Slider Control), then put on this expression:
wiggle(effect(“Slider Control”)(“Slider”),effect(“Slider Control”)(“Slider”))
You could have gotten there from your expression:
wiggle(30,30)
by hitting “e” to expose the slider, hitting “ee” to expose your original expression, wiggle (30,30), highlighting(select) one of the 30’s, then pickwhip to the slider, then doing the same for the other 30).
Setting a keyframe on the slider for 0, then 30 down the line will make the layer go from 0 to 30 wiggle-wise (not exactly ease, I’m still fiddling with that.)