I'm looking at heart rate variability (HRV). Frequently, in the Fourier transform I see two peaks that are close together. How could I determine whether this is two peaks, or just one peak and noise? Please see figure below. The units of the x axis is hertz. Thanks.

ps. I take a forty minute HRV measurement. For the figure below, I used a window of 1000 points, about 17 minutes, in the middle of the measurement. I'm not doing anything else to the data.

Below is also 100 data points from the source data.

[![enter image description here](https://i.stack.imgur.com/PWUdN.png)](https://i.stack.imgur.com/PWUdN.png)

[![enter image description here](https://i.stack.imgur.com/I0r5x.png)](https://i.stack.imgur.com/I0r5x.png)