I've noticed most people complaining about this problem have had manuals but I have an '05 auto and I don't think theres a specific speed it happens, it's more so when i'm trying to keep a constant speed... If i'm accelerating or slowing down it disappears, but i'll definitely be trying the aforementioned fixes to see if it helps... I've had my car for two years and it hasn't really got worse, i've just learned to avoid it but when my missus drives my car it's almost unbearable...