i had the same problem last week with my E4.5, so i saw your question today here.
I guess you may have solved your problem or have purchased new speakers already, i wanted to tell you, that i have solved the problem by opening the main (left) speaker. I found that the white connector which is on the main board connencting it to the volume control of the speaker at the front, was bruised with some yellow, brown mass on it. I think it´s from the production process and has flown into the connections. After disconnecting, cleaning it and re-connecting, everything was fine and the left speaker got the signal again.