I believe what you are hearing is a tape splice, or at least that's what it sounds like on my system. Most likely, the engineer recorded several drum solos and the "best" solo was then spliced into the "best" piano recording. Typical studio trickery!
On a highly resolving system you can also hear the tempo change when the drum solo is "plugged in" and then again after the solo finishes.
It sounds like your tweaks may have made your system more resolving!
On a highly resolving system you can also hear the tempo change when the drum solo is "plugged in" and then again after the solo finishes.
It sounds like your tweaks may have made your system more resolving!