Mystery (to me) clicks in Recording function

[farreln]

I have tried the Record function on MacBook and on iPhone (identical results). Every recording contains semi-regular light clicks throughout the duration of the recording. These clicks are NOT the count-in beats which are distinct and stop after 8 beats. The clicks are almost rhythmic but not quite. I am just making a backup-track to use in a DAW (GarageBand) so all audio inputs to the MacBook (and the iPhone for that matter) are set hard to zero. I start the recording and step away from the computer until it is complete so I don't believe I am causing any static electricity snap crackle pop.

Any ideas as it is a mystery to me.

Thanks, Norman