It's not always better to use the active voice. However, your sentence can be written as
The rattling sound of her washing machine woke Sophia up.
The rattling sound of Sophia's washing machine woke her up.
(You need to decide where in the sentence it is best to name Sophia)
In the passive sentence, what caused Sophia to wake up is the rattling sound of her washing machine, so that needs to be the subject of an active-voice sentence.
Peter Shor's comment at the linked question is valid and important, and I'm going to add it here:
There is a myth that you should never use the passive voice in good writing, and this is why MS-Word complains. This myth is completely wrong. You should use the passive voice to emphasize the object of a sentence, to make a sentence connect better with the previous or the following sentence, and maybe to vary the structure of your sentences so they aren't all the same (although this shouldn't happen if you use the passive voice when it's needed).
In the example sentence in the question, which is most important and should receive the emphasis? Is it the washing machine [in which case, use the active voice]; or is it Sophia?
I will also add that even if it's Sophia, you could still use the active voice so that you stop mentioning the washing machine as soon as possible and can concentrate on Sophia:
The rattling sound of her washing machine woke Sophia up. Irritated, she buried her head under the pillow and sighed noisily.