References haven't responded...how do I follow-up without being annoying?

I actually emailed three different references last week. They didn’t respond so I waited one week so I can be respectful of their time. Also we have a very good relationship and they said that I can use them as references anytime.

Seven days have passed and I still haven’t heard back. So I plan to send a follow-up but I just don’t want to annoy them.

How do I go about doing this?

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