I see there is so much interest in this subject and quite a bit of confusion about grounding that I thought I had to clear up something - it is important.
Grounding is implemented for electical things for safety purpose only. When there is electrical leakages, the ground cable brings the electricity to the ground and not to your body.
Grounding was never made to reduce noise in your amplifier! It is poor grounding (by many reasons, eg. poor wiring in the building), or, poor equipment design, that grounding is required to get rid of noise (or to some people in some situation, it increases noise).
There are 2 voltage systems used in the world - 100/110v in USA, Japan, etc., and 220/240v in Europe and Singapore...
Amps used in USA/Japan only often do not require grounding (ie. 3-pin plug) because the possibiility of killing someone is not high with leakages. But try holding a live wire in Singapore and you'll be dead soon.
Some amps we get here has no grounding (ie. 2 wires only connected to electrical outlet). This is quite scary because guitars power ratings are high, and when there is leakages it is dangerous! There was a guitarist from local well-known band who was killed this way in the late 70's. Many low-power equipment like DVD player, etc., usually comes without grounding as they consume low power and not that dangerous.
To ground an amp (that comes with 2-wire only), one way is to change to a 3-pin local power plug, and use a electrical cable to connect from the ground terminal in the plug to the metal part of the amp(a good place is the screws that hold the various parts of the amp together). Remember the screw should be on a metal part.
European equipment usually come with 3 wires, just cut off the Europe 2-pin plug and replace it with local ones.
Why after grounding, the noise level increases? - this is another subject...
Your safety comes first - when there is no life, there is no noise...
If you are still confuse, please get someone to alter the grounding for you...