Definitely fix this now Mihn. You can test it by putting one probe of a voltmeter in the sump, and attach the other end to your heater vent, or the ground-prong in an outlet, or any nearby metal house plumbing. Then plug each item into the wall, one at a time, and unplug it, then do the next one. One (or more) items, when plugged in will probably cause the voltmeter to read a voltage potential. Discard those appliances.
I'm no electrician, but I think the carpet static is a dangerous rationalization. If you're getting a constant tingle from your tank, it's definitely not static discharge. Walk across the room on the carpet and touch a door knob. That's instantaneous spark is static discharge, but if you hold your hand on the knob do you get a continuous tingling feel? No. Because static charge isn't a flowing stream of electricity, it's just an instantaneous equalization between two things that have an imbalance of electrons. You pick up electrons from the wool as you shuffle across the rug, so you're more electron-rich than the doorknob, and touching it causes you to quickly donate some electrons to the metal knob.
When there's a constant supply of extra electrons flowing into your tank, you don't get an instantaneous zap, but rather a continuous buzzing feeling for as long as you keep your hand in the water and your feet on the ground. While the light tingling isn't necessarily dangerous, it's a sure sign that an underwater electrical appliance is broken, and it's a good bet that it could get worse and become very dangerous to you, or even electrocute you right now if you were to touch it directly (ie, move a faulty powerhead in the tank). So I wouldn't ignore these issues or try to explain them away. Figure them out and fix them.
One more anecdote to add to everyone's above - these problems aren't isolated to the electrical appliances inside your tank. I touched a large fan that hangs about a foot over my sump the other day, and I got that same tingling feeling from the PLASTIC housing that surrounds the fan! The fan had collected enough wet salt spray on it's housing, that current could be carried across the entirely plastic enclosure of the fan to ground through my body. I replaced it with another fan, but I'm not sure how I'll prevent this problem from recuring in the future. Any ideas?
