I have noticed that in some accents the "r" sound is more trilled. But does this happen in every accent?
In this video I cannot tell any difference between the two.
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The main difference between rauchen and brauchen is the r is at the beginning of the syllable in rauchen. If so, it has to make a sound. There aren't any silent sounds in German pronounciation.
In brauchen however, the r can become almost silent, a lot of speakers will simple aspirate it, making it sound as ch. Other speakers use the same r as at the beginning of a syllable.
It's more a matter of personal preference than of dialect, but southern speakers may even roll the r.