Please correct my English text. Sequence of tenses always makes me confused.
While the teacher was speaking online, there was some noise as if someone was vacumming behind him. I didn't know where the noise came from.

Question

Please correct my English text.  Sequence of tenses always makes me confused.
While the teacher was speaking online, there was some noise as if someone was vacumming behind him.  I didn't know where the noise came from.

Answer

@Marsha: "vacumming behind him" 这里是“在老师身后使用吸尘器“

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While the teacher was speaking online, there was some noise as if someone was vacuuming behind him. I didn't know where the noise WAS COMING from.

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Could you please what the meaning of  "vacumming behind him" is?

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When the teacher was chatting online, I could hear some noise coming from behind him, as if someone was there using a vacuum cleaner. I couldn't tell where the noise was coming from from.

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There is nothing to correct really. This is perfect except for 'vacuuming'