so while sitting in my truck with the windows up a week ago I noticed this knocking sound, it's fairly faint and is always always At a consistent Rhythm. Meaning if the truck is idling, in or out of gear, or while accelerating or decelerating (although it's hard to hear then) it's the same sound. It can be heard in the cab or towards the back of the truck, but not the front or under the truck near the engine. Being that it doesn't correlate with RPM I doubt it's engine related but it just doesn't let up, and I'm just very curious what it could be. Any ideas?