Ok so I'm trying to help a friend out here and I need some help trying to figure out what's going on with his Z. His car starts making a knocking sound from the front of the car when it's at 55-75 ish mph and I can't figure out why it would do that. It makes the noise no matter what gear he's in and it doesn't get progressively louder or faster. Any clues?? Me and him are stumped