I tried posting this in Problems and fixes to no avail. Hope it's OK to try it here:

I've had my '08 TL-S for a few months now, and I've noticed that when I'm driving at highway speeds in certain wind conditions I hear a hum or vibrating noise coming from the back seat area. Yesterday I had rear seat passenger who said he could feel the plastic housing around the third brake light vibrating when the noise was happening! I'm wondering if it has something to do with the XM radio antenna or not. The cover on the roof does not seem to be loose.

Any suggestions?
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have some one (a good trusting driver) test drive it at highway speeds while you sit in the back seat and listen for yourself.. it'll be easier to evaluate it at that point.

 

are you sure it's not the active noise cancellation?

 

Good suggestion, ricgrrarrow, I'll give that a try!

No, bryanlee81, I'm not sure, but my passenger said he could feel the third brake light inside cover vibrate when the noise was present.

I just thought that someone may have heard a similar noise in that area and found out what the cause was! Maybe it is the noise cancellation? It's a fairly high pitched howling noise.

 

haha maybe it's a wild pack of unicorns dancing around up there