Remove "The post … appeared first on …"

Hello,

I noticed that some words have started appearing in my rss feed items: “The post (name) appeared first on (my site)”

I guess this happened through some update. Trouble is, it kinda messes with my mailchimp rss-driven email campaign.

I had a look at how I could get rid of it, and was directed to the wp-includes directory. I ran a quick search on all the files in that, and in none of the files are the words “appeared first on”. So it’s not just a simple delete sentence hack.

Can anyone help me get rid of this sentence? Thank you so much.