I have/ had the same issue only a month after purchasing the Airpods, so I contacted Apple CS via phone, which was actually helpful.
TL;DR: It was only one of the Airpods that produced the issue, we figured out which one it was, changed the mic setting to the other as an ad-hoc solution and I will have them repaired/ exchanged as a long term solution.
If your Airpods are connected, go to settings-->bluetooth and click in the little (i) next to them. Under "microphone" you have the options "Automatically Switch Airpods" or to have the mic always on the left or the right one.
Go on a phone call with someone as a test call and go out to a noisy environment (train station, busy street, kindergarten...). Speak with them as e.g. cars pass and let them give you feedback on how well they could hear you and the ambient noise while you go through the different options (especially left and right).
For me, this lead to me knowing that only my right airpod produced the issue. I will bring it in to a certified retailer of Apple, they will conduct a "sound check" on it to confirm the issue and then repair or replace them.
For now, I have switched to always have the mic on the left Airpod and I haven't had any complaints.
Hope it works for you!