Anyone had any experience with this? A slight popping sound is coming from the right rear window- maybe even the C pillar? It's hard to tell. I am reluctant to start pulling trim pieces but the sound is starting to annoy me.

This is 100% not the sun roof knocking sound, as I know what that sounds like.

 

I had the same issue in my 2012 XJL Supercharged 5.0 and it was noticeable when going over bumps on one side, basically whenever the body was put in an unlevel situation.
I could never figure it out and the dealer kept it a week and couldn't figure it out.
I'm sure there are more people with this issue and don't realize it due to the radio playing loud, traffic, or thinking it's something else.

 

It almost sounds like the rear window is loose or something. But it isn't. A very odd sound that is starting to bother me.

 

Could it be coming from inside that door? And is the noise/sound related to going over bumps, etc?

 

It is definitely coming from behind the rear door, somewhere in that "pocket" between rear window, and rear speaker.

The odd thing is that it doesn't happen (or maybe just isn't heard) over large bumps. It only is apparent over smaller, more rapid bumps that cause vibration rather than shock. It's apparent when riding over series of small cracks in a pavement, not over railroad tracks.

 

Yep, I had to revisit the dealership and drive the car with them to show the noise. It made it before we even got out of the dealership.
My thought was the rear partial but I'm not sure.

 

I think the first thing I'd try would be some silicone spray on the door seals.

 

I had some creeking noise and it turned out to be a door and window seal. I got this and it has fixed it once and for all.

 

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​​​It's a simple job removing the C-pillar trim and from your description, that's where I'd start. It may be that just doing that and replacing it will cure it. Otherwise, there are other bits and pieces behind there which may have worked themselves loose.

 

Interesting, as I already have this stuff, I'll try it out. It doesn't sound like it's coming from the door, more the rear window. But it doesn't hurt to try.

 

I have finally found and fixed the issue. Difficult to diagnose as it would be so obnoxious sometimes, and then quiet for a week. It was the plastic trim surround on the rear sunroof. Some foam backing completely stops the issue.