or while the neck sat with no tension on it overnight, the truss rod bowed it a little bit more than intended. I'd suggest sighting down the neck on both the treble and bass side to see if there is any relief(generally around 7-12-15ish). What it sounds like to me is that you're bottoming out due to too little relief. Also, check your saddle heights to ensure that they somehow didn't end up out of their seat or lowered in any fashion. It just sounds as if your strings are just bottoming out on the frets until you hit the frets that are relieved. As you mentioned, it stops above the 8th fret. If you don't know how to mess with the truss rod, either take it to a shop or read up on some of the posts here about it. Do a search. Basically, only work in small turns. more than a half a turn is usually frowned upon, as it could "damage the neck" Just be careful, use common sense.