Hi, i didnt realize this was all recorded by volunteers. Whoa! A Huge Mòran Tang! to all. Im thrilled to have the opportunity to learn Gàidhlig, and i appreciate hearing the variations. I also get Deb's frustration, Lots of new sounds. Perhaps a note somewhere so folks know all this? (I'm a tech peasant, so maybe i'm the only person this applies to, but after a year with Duo, i only just discovered there are notes/tips if i get myself to a computer). Mostly, tho, many many thanks for doing this!
You can also get to them via your phone's browser. If you're using the phone app, clicking the below link will open this lesson's tips there: https://www.duolingo.com/skill/gd/Rain/tips-and-notes
I am just a beginner, so take my comment with a lot of salt. I do hear the "i" too. I'm of the opinion it's one of the extra sounds native users use for the "flow" of the language. But I do hear the "i" too and it throws me every single time. If it were an exam question I'd fail.
Reòthadh is a noun, so "A bheil reòthadh ann?" asks whether physical frost is present. Frosty is an adjective, so "is it frosty?" might just mean "is it very cold?", or is it otherwise frost-like -- perhaps, is everyone angry and not talking to each other. Since we don't know the context, and since this is also a language course, we need to be precise.