Use of external flash reduce noise ?

"does the use of external flash gun will overcome the problem of noise?"

It possibly might, if you are using a flash with stronger output than your built-in.

"should i use the long shutter speed to intake more light in the camera for better results[?]"

Probably not. With flash, the light is created in an instant. The shutter speed needs to be somewhere between 1/60–1/250th of a second: long enough for the flash to occur while the shutter is fully open, and short enough that there isn't any visible motion blur from being exposed too long.

As the others mention, you need a low ISO to obtain the least noise. However, if you're shooting with flash, there already isn't much light to begin with, and the lower sensitivity can mean a dim image. You have to accept some level of image noise when shooting with flash. In many situations, only stronger studio flash units are capable of producing enough light to shoot at the lowest ISO available.

Noise is cause by high ISO settings.

In auto mode, you usually don't have control over the ISO being used, but some cameras do allow a bit of flexibility in setting ISO in auto mode... not familiar enough with your camera to tell you if yours does or not.

When using a strobe, the potential should be there to have low noise photos, however, this is still controlled by the ISO setting. The strobe will produce more light allowing your camera to use lower ISOs, but if the camera doesn't take advantage of that, then you are still going to get noise.

Your best solution is to learn how to use your camera out of auto mode so that you can control the ISO and thus the noise.

Same thing with long shutter speeds. It can produce low-noise photos, but again, only if the ISO is at the lower settings.

You should be getting the idea that you should always use the lowest ISO you can in any given situation.

Also, each camera model has it's own personality, and you should over time be able to realize how high of an ISO you can use before getting into objectionable noise.

Because your pop-up flash is so puny the auto setting is selecting high ISO to ensure correct exposure.

An external speedlite such as a Speedlite 430EX or 580EX will give more illumination.

Really you need to get out of "camera knows best" auto mode and start controlling the camera yourself.

When using flash, don't use a high ISO. To avoid seeing noise, don't zoom in when viewing the picture.

Try this, it's what I normally do.

Go to your manual settings and enter 1/200 for your shutter speed, f/5.6 for your aperture and have your ISO set at 100 manually and leave it there.

When you're in flash situations switch to manual, the settings above will be there if you've set them. Pop your flash, stand about 6 to 8 feet from your subject and fire.

It should work.

What's probably happening to you is that the camera, when in auto, wants to go to 1/60 at the shutter and about f/6 or 7 or more on the aperture. What you're probably seeing is camera movement from your hands. At 1/200 you should be able to avoid that.