Don't know if you mean the following: you're standing in front of the traffic lights waiting and after a few moments you feel some sort of thud (difficult to describe but it's some sort of tender shiver or shrug - only once), as if the engine settles. That's what I sometimes experience too. No idea why. Noticed that, but thought that it's normal.
“For ’tis the mind that makes the body rich” (W. Shakespeare, The Taming of the Shrew, Act 4, Scene 3)