If you hear difference it can be perceived as improvement (already mentioned).
If you anticipate difference, it can result in bias to expect improvement (already mentioned).
If you hear even slight increase in gain/volume, it can be perceived as improvement (mentioned elsewhere).
What’s usually not mentioned: there’s a reason real research relies on controlled testing and sample sizes > 1.
If other folks who can’t see what’s being used (only 1 factor changed per trial) aren’t able to predict reliably, you’re probably imagining any perceived difference.
If you cannot see what’s being played and aren’t able to predict reliably, you’re definitely imagining any perceived difference.
If either of those results fail to apply (i.e., properly controlled trial results are consistently predicted), you can perhaps reject your null assumption of “no difference” between…
But most folks can’t be bothered with that level of rigor in their “testing,” feel convinced without real evidence, and profess their impressions as transferable realities.
So ignorance can be contagious bliss. And it can also get pretty expensive. 😉