Strange noise from the engine suddenly

[PanRider1300]

I need your help guys. After a drive with my wife as passenger the engine makes a different noise. Even my wife said it when we stopped.
It sounds like a heavy rumble. It is not the high pitch sound. It is deeper. As if the engine have more difficulty to turn around.
But it reacts good with throttle.

The spark plus are new. Original NGK iridium.
I have changed the coils to test if their is one faulty. Not.
New oil and filter.
All the vacuum tubes are new. Nothing clogged.
I even have the throttlebody synced. I thought maybe to much out of sync. But that was not the case.

I have made a video. The sound is good, but it is not so clear to hear.

Thanks

 

[JetRanger]

I'm far from an expert but it sounds like knocking due to bad or low octane gas.

Did you refuel on your trip?

 

[Igofar]

Pull the NGK Iridium plugs out!
There are so many knock off, fake plugs out there that NGK has a page showing how to tell if they are real or not.
I have a large jar of fake/knock off NGK plugs that folks purchased, brought to me to install, then NGK verified that they were not the real product.
IF they are fake, they can damage your engine.
This would be the very first thing I would inspect/check.

 

[bdalameda]

It sounds a lot like cam chain noise.

 

[forestfarm]

I always get my NGK plugs directly from NGK .so many fake crap ones on amazon and ebay.Good price too!!