Creaking noise under passenger taillight

[number9ine]

A few weeks ago, I noticed a creaking noise from the back of my car (05 C2S). I'm not sure precisely where or what it is, but it sounds like it's coming from directly under the passenger tail lamp. The sound is a higher-pitched version of what you hear when you walk on an old floorboard. It's not audible under normal driving, but if I hit a bad bump I hear it. I can also push on the rear glass or remove the tail lamp and press there to hear it.

I plan on pulling the bumper cover and having a closer look underneath this weekend. In the meantime, If you've seen or heard about something like this before please chime in. Searching here really hasn't gotten me anything close. Thanks!

Mark

[RFM]

A loose welding point is sometimes the cause, but difficult to pin point. Success.

[number9ine]

A loose welding point is sometimes the cause, but difficult to pin point. Success.

That sounds ugly. Hopefully I'll find it, will update if I do.