Early into the episode Phoebe comes into Central Perks coffee shop and talks to Monica and Chandler. After Phoebe says she can't find a word to rhyme with the yelling sound she makes the audience laughs. As the audience laughs you can clearly hear the director say "cut" right before going to the next scene.
In the opening scene of this episode Joey tries to spin the basketball on his finger and spins the ball into a lamp and off the end table. In the next shot Chandler and Ross are sitting on the couch and you can see the ball roll behind them onto the couch, at the same time you can hear the ball bouncing on the ground away from the table.
When Mike's friend Manny rushes into Phoebe's apartment he dismissively tells Monica that he heard Mike's emotional speech, but that is unlikely as he would need to be in the apartment or listening through the door to hear it, which he quite clearly was not.
Phoebe wouldn't have buzzed Monica into the building if she knew Mike was on his way to see her.