Yer' gettin zapped by good ol' ESD! (Electro-Static Discharge).
Would have imagined that wearing only socks wouldn't build up a high charge (the socks wouldn't scrape charges off the carpet like the sole of a shoe or slipper will), however, the socks are most likely made of the same material as shoe and slipper soles (HDPE, rubberized nylon or polyester, ???) and this would scrape the Carpet when you take a step, pulling off some negative charges in the process.
Whatever the material is, it's obviously more Positive than the Carpet's material! - hence the "TICK"-OWWWCH
experienced when touching something metallic.
Must be dry and possibly windy in your area (or your heater is really kicking A*%).
Before I go too much farther, you are certain this is not a 120 VAC bite??? I know this is a silly Q, but it's possible.
Fun stuff to do with ESD (besides discharging yourself into the nearest person... hee-hee):
Get a fairly new Fluorescent Tube - like an F32 T-8 (I have been successful with the older model F40 T-12 "Energy Savers" - 34 watts and 4100 K color / cool white).
Turn off lights and / or close curtains - making the room as dark as possible.
Put on your most "Shocking" shoes (any shoes that you own which cause ESD just by being near the carpet
With the room dark, the shocking shoes on and the T-# Lamp held near one end, start scraping your feet really hard on the carpet (just don't let your wife see this, or she may use the T-# lamp in another fashion! :eek
While you scrape your feet, the lamp will glow. See how far up the tube you can get the glow to go, and also how bright you can get it.
After doing this, join a social club - you have way too much free time on your hands
First experience of this for me was on an office complex which was inside a warm and dry Tilt-Up building, plus during a Warm Santa Ana condition (Santa Ana winds).
The rooms had just been carpeted with the typical glue down low pile Commercial carpet.
I was Lamping 2x4s in offices when first noticed the glowing lamp situation.
That was a really shockee day! Was so strong at times I could blast a good 1/16" wide arc onto something / someone (OWWW!!!).