Here is my signal chain : Maxon od(no gain only boost) > line 6 m5(working as a noise gate decay at 0 and threshold at 30%) > AMT preamp. I get no noise when the amt is on but whenever I engage the maxon I get some noise(which is expected due to the increase in gain) so I decided to use the m5 as a noise gate but the issue I face is noise( sounds like woshh) when I roll the volume down, it lasts for 2 seconds. Increasing the decay obviously increases the times the woshh noise needs to fade. Is it due to the fact that the m5's noise gate doesn't react quickly? Will a noise gate like the boss ns-2 or isp decimator solve it? I don't have any ground loops or that kind of outside noise.
Firstly I'm going to refer to your noise as hiss, even if it isn't a hissy sound.
I'm not going to promise that a Boss Noise gate or other product will solve the solution but it will definitely be a better option because its not modelling a noise gate and actually is one, so will function as such. As for the hiss I've not used this noise gate myself however its possible that its simply set to still allow the addition noise through. Here is my first guess:
If that didn't work then here is my second guess:
Hope I helped, not my strongest subject but I gave it my best shot.
The main difference between noise gates, whether they are modelled or direct, is their performance on increasing volume and decreasing volume.
It sounds like in this case you are coming up against the M5's relatively long decay - in which case a dedicated noise gate will definitely improve things.
In addition, a dedicated analogue noise gate doesn't have to worry about digitising the signal and passing that through various changes, it simply applies a dramatic cut based on the volume, so you don't get weird audio artifacts appearing.