I've installed a foxskyline valvetronic exhaust system. After installation whoo that coyote's loud. A few months later i noticed it got quiet and thought it was just me getting used to it. Now here's the catch. If the car starts with the switch of valve positioned on open the coyote doesn't roar as loud as it used to but when I drive a little with the valve closed for 10 minutes then reopen the valves the sound gets louder. It's weird how I need to drive with the valve closed for a few minutes then the sound gets louder (the muffler pops from the tune). I was wondering if it's a faulty valve, something to do with temperature/humidity, or electronic issues such as bad wiring (melted wires), wiring goes from the battery towards inside the cabin and connected to a switch that I've place near the steering wheel. Any suggestion?
Side Note: I'm certain I'm not getting used to the sound because when I close the valve for a little bit (then fuel starts popping in the muffler) and when I reopen the valve it's louder and more aggressive.
For Ref. 2017 F150 5.0

 

Can’t really help but the exhaust sounds interesting. Any links to where you purchased?

Edit: have you thought about mounting a GoPro at the valve actuator arm and see if it opens (extends) to different lengths when you notice the volume change? Indicating if it’s opening the same amount in each instance

 

Doesn't require a go pro... crawl under the vehicle (when cold), mark the shaft, hit the switch, then see if it rotated 90º.