Sound got quiet in the middle of listening to an album and now I have to turn my amp up much higher than I had to before.

Was in the middle of a listening session and all of a sudden the music got a lot quieter. I went to see what happened and now I have to turn the volume dial way up to get a good volume. It also doesn't sound quite as clear as it did before. Did something in the amp go bad?

System being used is a Fluance RT85 TT, Onkyo A-9010 amplifier running through the phono input and KEF Q150 speakers. I got the amplifier used, but it's worked perfectly for a few days now since I got it. Just sounds not as good now after whatever happened. Bass isn't as clear and it seems like I need to crank it to around 80% to get a listening volume. Treble is more tinny.