how to get rid of pops??

I recently recorded a guitar player and he wanted to hear the sound with effects when he recorded, so for the 1st time I recorded tracks with the ‘monitor’ on which I never did before. Thought this was a great discovery now a guitar player does not need to hear a dry sound during performance. Then when I exported a mix, you hear pops which seem to be related to when the guitar tracks enter, like an electric pulse like someone turned on or off the electricity for a second (when the track begins)…have no idea what it is…im a novice…its probably something simple…can anyone help?..btw…i have recorded for years and never had this issue…so it must be because of the monitor recording…is there a simple solution?