For me it’s a vowel sound, sure, but the mouth is definitely in, or moves to, the position it would be if a pronounced R, and presumably a vowel, was about to follow.
Probably more so than in the pronunciation of name of the letter R itself, in fact, which is indistinguishable from “ah”.
But perhaps more importantly, no, we generally don’t say “brr” anyway, except in exaggeration or for effect. You’re more likely to hear something like “it’s bl–dy freezing” or “my hands/feet are like ice”.
For me it’s a vowel sound, sure, but the mouth is definitely in, or moves to, the position it would be if a pronounced R, and presumably a vowel, was about to follow.
Probably more so than in the pronunciation of name of the letter R itself, in fact, which is indistinguishable from “ah”.
But perhaps more importantly, no, we generally don’t say “brr” anyway, except in exaggeration or for effect. You’re more likely to hear something like “it’s bl–dy freezing” or “my hands/feet are like ice”.