single pop sound when first touch pedal or guitar string

[PCR]

When using an effect pedal with a metal case, is it "normal" to get a single "pop" sound when touching, with your fingers,  the pedal or guitar string for the first time or after a few minutes of not touching it?  It seems like a static charge discharging. 

[amptramp]

Do you feel any static shock or power line shock when this happens?  Static shock is usually not dangerous but it can happen with a system that is not returned to a power line ground anywhere.  BTW, what pedal is it and is it your build or a commercial one?

[PCR]

Thanks so much for replying amptramp!

No I don't feel any static or power line shock.  The pedal is one that I have built which has an I/C buffer into a Peppermill overdrive circuit from Runoff Groove into an AMZ mosfet booster circuit.  The overdrive and booster circuits are true bypassed switchable.  The pedal runs off of my rechargeable 18V ryobi lithium ion batteries. The battery feeds a 9v i/c regulator which powers the 3 circuits.   The amp is 3 prong plugged and properly grounded.

Is this pop something I should be concerned about?