// Looping Wiggle Expression in After Effects
// Option + Click Position Property
// Source: MotionScript.com http://motionscript.com/design-guide/looping-wiggle.html

freq = 1;
amp = 110;
loopTime = 3;
t = time % loopTime;
wiggle1 = wiggle(freq, amp, 1, 0.5, t);
wiggle2 = wiggle(freq, amp, 1, 0.5, t - loopTime);
linear(t, 0,  loopTime, wiggle1, wiggle2)

// Simple Wiggle Expression

wiggle(3, 10); // frequency, amplitude

// Right click on layer > Choose ‘copy expression only’ and paste on other layers as needed

// Continuous linear loop

time*10

// Loop Expression

1. cycle (default)
2. pingpong
3. continue
4. offset (stepping motion)

loopOut("cycle");  // Will repeat after last keyframe
loopIn("cycle");   // Will repeat before the first keyframe

More complex resource: https://www.schoolofmotion.com/blog/amazing-expressions-in-after-effects

More complex resource: https://www.schoolofmotion.com/blog/time-expression-after-effects