Gritty White Globules in Precooked Grocery Store Sausage?
Largish white bits like that will be either fat, cartilage, or (other) connective tissue. Once cooked, if they can be squished apart with your fingers they're fat; if they're crunchy when you bite into them they're cartilage; if they're very chewy they're connective tissue.

Fat should be quite soft once the sausages are cooked to a safe temperature, so I assume they're not that. The other substances get their structure primarily or entirely from collagen, which will break down during long, slow cooking, but that's not a normal way to cook a sausage and will probably result in a dry, grainy texture overall. If they're a problem, I would suggest trying a different brand rather than trying to cook them differently.