https://www.cnn.com/2019/10/19/politics/impeachment-poll-of-the-week/index.html
When Quinnipiac polled about the inquiry from September 27 to 29, 52% approved of it. From October 4 to 7, 53% approved. Now, 51% approved.
CBS News/YouGov polling shows a similar trend. On September 26 to 27, 55% approved of the impeachment inquiry. From October 8 to 11, it was 53%.
Marist College did a one-day poll on September 25 and put support for the inquiry at 49% among all adults. When it polled from October 3 to 8, that jumped to 52%.