Exhaust popping on decel

It's always done this but seems worse this year than last. Literally sounds like a shotgun sometimes.
Ive put 2/3rds of a tank of fresh petrol in it since last November, and a bottle of Redex. Im wondering if the old and new fuel mix is causing the popping? It's only started since riding this year and i've made no modifications since then.
It also hunts slightly at idle, but it seems increasing the idle speed has done away with that.

A bottle of redex? You are joking I hope? That will do not a lot EasyDuz & it's probably why it's poppin n bangin on the over run?

As Peter says far too much redex, a couple of cap fulls is enough, for the size of the tank.

It was doing it before the Redex was put in. I thought a long ride would fix it but it hadnt so I put the redex in after.

Is your bike carbed as I can not remember what year it is, if so, does it have stock exhausts and stock air filter?? If not has the carbs been re-jetted?? or ECU re-mapped if Fuel Injected?? When was the last time the carbs (or even throttle bodies) were balanced??
A bottle of Redex will not help matters - "One shot of Redex fuel cleaner is capable of treating a fifty-litre fuel tank, but those who have never used a fuel additive before – or those who own an older car – may wish to use two shots for an intensive clean, particularly during first application". The VL I think has about a 18l tank so you may have overdone it a tad

Check that the exhaust manifold bolts are tight also check clamps where silencers connect. My VZ was popping  badly on the over run, when I was cleaning the bike I noticed one of the nuts missing from the manifold. New nut fitted and torqued up, no more popping.

Literally nothing has changed since last season where the bike didnt pop on decel, now it does.
Its FI, manifold bolts are tight, no signs of a leak. It hadnt even been moved from November to March, now its popping and banging

I'd start by draining out the fuel - if you didn't use a fuel stabiliser before winter, there's a chance it could be stale fuel, although you have watered it down quite a bit.  I use Briggs & Stratton Fresh Start, I buy it from a mower supplier - it also contains an ethanol inhibitor - something you need to watch out for on an older machine. I always add some to my tank from around November onward when I know I'm not going to be going through as much fuel.

Ill run it until the light is on then fill with fresh premium. Maybe the valves need adjusting? Its approaching 14000 miles I think

I liked the sound of it when mine randomly started popping :) Im putting a new Vance and Hines Straightshot exhaust on it anyway so let's see the difference in sound now