Same experience with you. I have 2 setting in my HU. 1 for the morning. 1 for afternoon and evening. At night normally dont drive, so never set

I thought only tube amp got such setback ? Solid state also the same ?
Other reasons I pluck out of the air to justify (read:"bluff you"

) are :
1. Speed of sound is measured at 20 degree C. If you car parked under the sun, it could go up to 50-70 degree C. So, the setting you made during night would run a bit
2. Wire also the same for the above theory. So the SQ would be different also
3. Your ear drum sensitivity will change with heat
4. Speaker surround is normally made of rubber. With >50 degree heat, it would perform differently also
5. You would normally full blast your aircond during afternoon. So the SQ will be affected too
