I also have 2 (male) cats that do this! Could the "BBBrruuddtt-ing" be a learned sound? I ask only because these 2 cats are both adopted from a street cat rescue society, and they lived together in the foster home for a few months before I adopted them. They are not related. My 2 older (female) cats do not make this sound. They meouw normally. I really like the question mark sound at the end of the bbrruuddtt??