Hi, does anyone know of a channel failure problem with the 15" mono mbp? I have had the LH speaker replace under AppleCare but have just noticed the LH channel has once again disappeared. Plugging in the headphones gives me intermittent LH channel after wiggling the plug. wiggling however has no affect on the speaker output when the plug is removed?? The service centre initially said there was no problem with the speaker and I wonder if they changed it just in case? Any thoughts?? Thank You.