Hi, welcome to the forum!
Not sure... could be a connection at either end or pinched cable somewhere in between. Not sure, if the others are all working, if it would be at the headunit :? I've not heard of the speakers blowing either.
Would help to know which system you have? (EDIT - see un1eash's question below, this will tell us if you're not sure)
I think that channel is split between a mid range speaker and tweeter which is near the bottom of the A-pillar. Does the tweeter give any sound when you move the fader / balance to that "corner"?
If you trust their engineers I'd be inclined to tell them to get it fixed... although if you have any doubts, get the price down and get it to a specialist if you're not sure yourself - last thing you want are rattles because they've snapped a lug or not refitted something when chasing the cables through.
There's others on here that have a better handle on the AV side of things, but it would be handy to know which system and the tweeter output. There is definitely sound from the opposite speaker? I ask as on the standard HiFi there is an empty speaker box somewhere that's reserved for the upgraded HiFi.
You'd need someone local to comment on the costs.
