Why is samsung S21 making pulsing sound when running??

[cobaltB12]

I'm using Samsung Galaxy S21, Amazfit Bip U with Zepp to track my exercise, and 1more comfobuds pro for listening to music. This is the first time I'm running with the 1more comfobuds pro. During the run, I noticed a weird pulsing/whooshing sound that would intermittently sound 2 or 3 beats. Initially I thought it was low battery or something but this stopped once I ended the exercise. I've never heard this sound in day to day use of the comfobuds, even when I gym. But I don't track my gym workouts.

I can't figure out if the whooshing sound is from a weird setting for the comfobuds pro, from the S21, or from the Zepp/Mi Fit app??

Anyone had a similar problem before?

 

[Trees]

Maybe the Zepp app has a notification for when a specific heart rate, speed, or other metric threshold is reached? The whooshing sound could be headphones rubbing on a hat, or jacket hood (assuming you were wearing one)?