Cracking and distorted sound in Logic Pro X

Hi

I have mid 2012 MacBook Pro with 2,9 i7 prosessors and normal hd. I just upgraded from 8gb to full 16gb and I thought this might have resolved the problems I have been having with Logic Pro, but sadly no.

My problem is that I usually recored guitars home to the project that I have brought from our rehearsing space where we have recorded drums first and then I just recored guitars home using plugins. I rarely have any problems when recording but when I come back to listen the project the sound of guitars is distorted and cracking. I don't even use that many tracks to recored guitars, usually it is just one on left and one on right but it still can get messed up?

So does anyone knows what to do? I assume that It has something to do with plugins and cpu but with 16gb of ram you should be able to handle few plugins???

Or should is just get a new computer? Or maybe ssd? But I dont know if that ssd will help.

Thank you for any advise.