X's post

"She are single."

My post:

"I noticed/notice that you have made a grammatical mistake in your post. "

Which is the correct tense, past or present?
I notice that you have made a ... mistake... is the more consistent with regard to tenses.

In the past, for example, if you retell the story to a friend later,

I noticed that he had made a ... mistake ...

In my opinion, the tense of that statement depends upon the context of the rest of the message. It could be present tense (e.g., "Hmmm...now that I examine your message more closely, I notice that you....") or past tense (e.g., "As I was reading your message, I noticed that....").

However, I would most likely use past tense and rewrite your sentence as "I noticed a grammatical mistake in your post" or "I noticed a grammar mistake in your post."

Students: Are you brave enough to let our tutors analyse your pronunciation?
 CalifJim's reply was promoted to an answer.
Thank you, everyone.