In that case, your ears are probably getting tired of hearing that same riff over and over again. Once you give your ears a break and after they've had time to rest, something may sound totally different.
#1! Sounds like ear fatigue to me. It happens to me at gigs where the first few songs in a set sound really, really nice, and as things continue, the band sounds duller, even a bit too loud, or the drummer's cymbals start to irritate the ear with a nasty treble edge, etc. It's the effect of ear fatigue, caused by listening to music at a steady and high enough volume. It's why the better music producers won't start mixing an album until they can come in with fresh and rested ears, and are smart enough to take breaks as needed in the process.
I think its my strings, I need to replace them and buy some nickle ones. Ear fatigue sounds interesting too. I play loud sometimes along with music so maybe that might be it too. I don't know anything else it might be, it could be I need a more quality guitar.