Noisy System

Hi, wondering if anyone can help. My hot water is fine and central heating fine, however, for the past 2 days the system has been rather noisy. The sounds of water/air running through the pipes is constant and driving me mad! My heating is off, but I constantly hear this noise in radiators as well as the boiler and tank. I'll be honest I'm rather a novice at these things, but I've checked the pressure guage and the black bar is below zero with the red bar between 1 & 2. I'm not sure if I need to adjust this, vent the system etc and if this the likely reason for the noise. Any guidance would be gratefully received!

HI

The problem sounds as though it's just the low water pressure in the heating system.
The black needle is the important one and should read approx 1 - 1.5bar when the system is cold. The red needle is simply an indicator that could be is often set by the installer to show where the black one should go to when the pressure is correct.

Simply put the heating pressure back up to 1.5bar and that should do the trick.