Sorry, I missed that line in your original post.
Your friend's speakers(unamed, but let's assume the same as yours) hummed at your place. You've gone only half way; do yours hum at his place? Do his hum at his place? That's all the matrix you need to try.
Both hum, both places = design or production fault w/ both speaks.
Both hum, only your place = wiring problem, your place.
His don't, your's do hum, your place = defect in your speaks.
Your friend's speakers(unamed, but let's assume the same as yours) hummed at your place. You've gone only half way; do yours hum at his place? Do his hum at his place? That's all the matrix you need to try.
Both hum, both places = design or production fault w/ both speaks.
Both hum, only your place = wiring problem, your place.
His don't, your's do hum, your place = defect in your speaks.