"When I plug it in all the way, there is either muffled, or no sound at all."

That's a hardware failure. But since it's the 8400m chipset PLUS it's from the dv6000 line (which is the line, not your model) you want to do two google searches and call HP to correct this.

8400m defective

Then a search for:
dv6000 recall

Since HP fixes this by replacing the main board and reloads the OS then you get a short warranty you may get this fixed for free if you play your cards right.