Turn it up...?

@mapman     Agree.  Need to measure sound levels before jumping to subjective conclusions.

@imhififan      Unlikely voltage variations can cause this.  In UK +-6% variation is the legal maximum.  Most amps draw power and store it.  Once there is sufficient in store the amp will perform consistently.

I’m thinking it’s something else. I know my hearing is not the same when I get up in the morning as it is in the afternoon/evening.

All the best.

JD

Is your preamp/AV receiver set to night mode? That could explain.