x <- c("aaaaaaah" ,"aaaah","ahhhh","cooee","helloee","mmmm","noooo","ohhhh","oooaaah","ooooh","sshh","ummmmm","vroomm","whoopee","yippee")
grep(".*([a-z])\\1.*(?!\\1)([a-z])\\2", x, value=TRUE, perl=TRUE)
eCA8LSBjKCJhYWFhYWFhaCIgLCJhYWFhaCIsImFoaGhoIiwiY29vZWUiLCJoZWxsb2VlIiwibW1tbSIsIm5vb29vIiwib2hoaGgiLCJvb29hYWFoIiwib29vb2giLCJzc2hoIiwidW1tbW1tIiwidnJvb21tIiwid2hvb3BlZSIsInlpcHBlZSIpCmdyZXAoIi4qKFthLXpdKVxcMS4qKD8hXFwxKShbYS16XSlcXDIiLCB4LCB2YWx1ZT1UUlVFLCBwZXJsPVRSVUUp