Should the second character in 回来了 be pronounced with second or fourth tone? I almost always hear 来 pronounced as lài in 回来了, but are there any rules of tone sandhi that account for this?
I am a native speaker. The term 回来了 is of course pronounced with ㄏㄨㄟˊ ㄌㄞˊ ㄌㄜ˙, so the second character is pronounced with 2nd tone. And the word 来 can only be pronounced with 2nd tone. (I've never heard 4th tone.)