Lexus RX 2010-15 :: Car Rattle At A Certain Temperature Range

At a certain temperature range (just below freezing, -10C to 0C) I was getting a rattle that sounded like I had a cup of dice on the top of my dash. Any slight movement would cause the dice to jostle about, in other words the rattle was constant, the slightest bump or ripple in the road, slight speed up/slow down, even relatively flat roads would cause noise. It would come and go as the temperature changed but this last week the outside temperature has been consistently in that range, so therefore while driving anywhere I had to first head towards a place called "nuts". I'm not due for any service for a while, but it was getting to the point where I was prepared to make the long drive to the dealer. First though, I tried to hunt it down myself.

Spent last night with my head under the dash looking for anything that could be that loose to make noise so easily. I noticed the TPMS reset button unit sat kind of loosely in the lower dash panel, I could make a noise shifting it about, but it was just too light and too low down to make the noise I was hearing. I did the usual reaching around applying pressure to various parts of the dash while driving. Trying to listen carefully, I decided the sound was coming from the windshield (or deflecting off of it from the dash). I tried applying pressure to it, I even put a pair of socks on the end of a yard stick to I could put some pressure at various points along the windshield / dash area. No difference.

Finally, got a bit of a hint. On the highway, passing 60mph the rattle started to abate, getting close to 75 mph the rattle almost completely disappeared. Wind pressure? On inspecting the lower part of the windshield, wipers, etc. I notice that by shifting the plastic underneath the wiper arms it would make a noise. It doesn't feel very loose, it took some effort to slightly shift it, but it did make a noise. I took my "test socks" and jammed them under the hood directly in front of the wiper, creating some downward pressure on the plastic. Silence! Golden Silence!!