Breakdown of Ты включал пылесос? Я слышал шум.
я
I
ты
you (singular)
слышать
to hear
включать
to turn on (imperfective)
Questions & Answers about Ты включал пылесос? Я слышал шум.
Why is the imperfective verb включал used here instead of the perfective включил?
This is a classic example of the annulled result. By using the imperfective включал, the speaker is asking if you turned the vacuum cleaner on and then off again. If they had used the perfective включил, they would be asking if you turned it on and left it running, meaning it would still be on right now.
Could I use the perfective включил if the vacuum cleaner is still making noise?
Yes! If you walk into a room, hear a roaring vacuum, and want to know who turned it on, you would use the perfective. You are focused on the fact that the result (the vacuum being on) is still actively happening right now.
Why is слышал imperfective? Wouldn't hearing a specific noise be a single, completed action?
Verbs of perception like слышать (to hear) and видеть (to see) are typically used in the imperfective when simply stating the fact that you experienced a sound or sight in the past. The perfective услышал would heavily emphasize the sudden onset of the sound, meaning you suddenly caught or noticed the noise.