I just purchased a Master Lock #140D yesterday, so being that these two locks are fairly similar I thought I would share my observations. I know that the #140 I bought has two serrations on the driver pin in the #1 stack, so these clicks may very well be a serrated pin that you're brushing up against. Also, given that the pin stacks are probably closer together than on, say, a Schlage residential key-in-knob lock you might actually be hitting two stacks at once when you remove your pick.
On my 140 the serrated driver is the first pin to set. When pushing it up, I hear *click* *click* *pop* and the cylinder then rotates, snagging on the three remaining spools. From there its a game of very light tension and counter-rotation.
Hope that helps!