Why am I hearing crackling on my macbook pro laptop

Try using headphones or external speakers to see if the problem is with the audio in general or just the built-in speakers.

You don't mention the exact model Mac (very important info to have), but if it is an older Mac, then most likely the speakers are bad. I've seen an extraordinarily high rate of distorted speakers on the MBPro 2014 models (and 2015 as well).

My 16" MacBook Pro has a left speaker crackling. There's a long thread on macRumors regarding crackling of MacBook Pro speakers. I've seen one other post mentioning just the left speaker. When I plug in headphones, the headphone sound is clear.

However, I think this is a software issue. If I remove the two .plist files in the Audio folder (within Computer>Library), the crackling sound goes away for a period of time, not always, but sometimes.