Pongo, a 7 month old is a challenging age all by itself.
My 6 month old has all of his adult teeth now and has been biting anything and everything very hard. He is beginning to learn bite sensitivity and that is probably an additional factor in your story.
If a basenji changes behavior suddenly it is important to verify that your basenji isnt in pain or discomfort first. And, basenjis dont all show pain the same way. My female would just shake, my male would be very growly when he had a bladder infection.
I would suggest asking your vet to do a fecal, urine and blood test. You may also want to check his eyes as well. Trainers suggest massaging your dog all over and in the mouth to get them used to handeling. It is a good way to note any painful areas.
I can say it is very bizare behavior for a 7month old to growl and want to bite if you have had him since he was 8weeks without anything traumatic going on.
I do remember that around 7 months is when I began yelling, "no" at Caesar and he became far more difficult, never growling, but difficult. Socialing him in an obedience class with lots of other people and dogs would be a good way to work on training and how he addresses others (your rules). It also helped me understand and communicate with him.
Keep us posted.