Since there's no such thing as an original problem (whatever problem you may have, not only has someone had it before they've already posted it to the internet) I thought I'd ask if this has happened to anyone else here since a search didn't come up with anything.

Rattle only seems to be when stopped and idling at a light and putting my hand on the dash near the top of the steering wheel cures it, but I'm not sure of the cause or where to start diagnostics.

 

What manufacturer's windshield did you use? Your type of problem tends to occur when an aftermarket windshield is installed.
Another thing. https://www.aandaglass.com/signs-you...-is-incorrect/

 

I'm not a windshield installer and don't know about short cuts, etc., but I have read through the Lexus procedure for replacing the windshield. By the book, it definitely does NOT appear to be a SafeLite kind of deal.

 

I specifically requested (& paid for) PPG SOLAS glass, but didn't notice until the installer left that I got FUYAO glass instead.

I looked at the work order and it had the same part number as the PPG SOLAS glass I ordered from them 14 years ago, but the glass is from a different manufacturer.