The lips thing works even though it doesn't sound quite right, I use that method. My brother in law does it the other way which I "think" sounds better but when we would be out calling, if I purred the gobbler would keep in strut and gobble putting on a show, my brother in law thought he would try his hand at it. He purred, the gobbler dropped out of strut and ran. Even though he sounded better to my ears, the turkey was scared to death. It didn't sound aggressive but it must have been the tone that sent him packing for the hills. Do what you can with what you got.