Can he recognize his own feelings? Is he telling you he is frustrated? Does he recognize that he has options on how to deal with his frustration? Maybe he is that kind of kid, more sensitive to frustration, & is having a hard time knowing how to deal with it. Maybe, although I know how exhausting it can be to hear the whining as our daughter get frustrated easily too, it might help to help him try & work it through so that he learns how to mange these feelings & so that he learns what his options are when he is frustrated. Eg. he can express his frustration by saying "I'm frustrated." He can stop what he is doing & come back to it in a minute. He can maybe do a grunt & then approach it with new insight. Or maybe he can do a belly breath. These are all the techniques we are using for our daughter when she get frustrated. The hope for me is that with these techniques she will learn how to identify & manage her feelings herself rather than just whining. I hope this helps.
p.s. If you like what I am saying, I highly recommend checking out "Raising an emotionally intelligent Child." by Gottman. It is one of my top three parenting books. All gold.