Speaker Buzz after no. of tracks builds up - Pro Tools 12

[bighoneysqueeze]

Has anyone else had this issue?

I'm thinking my laptop specs aren't up to scratch. Once a session I'm working on (Pro Tools version 12) reaches a certain amount of tracks, usually about 15, a white noise-esque sound starts corrupting the playback and it's such a hindrance trying to arrange mix a piece with this harsh buzz going on. It's not present the whole time and I might find that I can continue working for about 30 minutes before it's back again ruining my life.
It could also be the interface but I've basically ruled that out seeing as the interface works perfectly up until a mix I'm working on has progressed significantly (in terms of size). Any advice / Input?

Thanks Guys.