Noise is a common occurence when setting up to record. The only way to fix this is to isolate the problem. It takes some troubleshooting though. It usually helps me to write down what I have tried so I wont get confused or overwelmed.

Some stuff to try:
If the gain is to high that could be a problem. You can fiddle with the input gain to the recorder and also, guitar and see how that affects things. Try another mixer channel input. Try to connect another instrument like keyboard or ?? and see if it goes away. Move the recorder to another room incase other equipment may be noisy. Try another guitar cord somtimes plug or wire are problem.
Its possible also, the noise is coming from the guitar. Bad grounding or wiring. Could also be noisy pickups. Google "guitar wiring" and there are a whole lot of sites that discuss this subject. If you have a friend with recording equipment you can plug in and see if the problem is still there.
Those are something to try. You will probably get more responses
Best Wishes

cheers, the problem is solved, must have been some noisy equipment cause it works great in other room, thank you so very much :D

I have a problem with some lights that use dimmer switches, and bad grounding. It really creates a lot of noise when these lights are on.