When I ever I sneak I hear this weird drumming sound, is there anyway to fix this?

This is not normal, so it may be a mod related issue.

If no mods, then try reducing the sound of the footsteps, and try going into third person and see if your character is operating a normal speed or sped up.

Finally, make sure there are no Scribs nearby or on the other side of the hill, then make a drumming sound that can be heard from quite far away.

A Google search tells me someone once had this problem and that it was caused by the Companion Gabby mod. Are you using that mod?

No, I do have mods.

Maybe I should disable all my mods and re-enable them one by one.

Try the 50-50 technique, it's much less time consuming. You turn half of your mods off and see if the problem persists. If yes, then you cut those mods in half and see which half has the problem etc.

I've found out that it's Companion Share and Recruit.

And I found a sound fix for it on the nexus!