I have a 1988 mustang gt, I've only owned it for about a month, it has the tremec t-5 tranny with pro 5.0 shifter. As I was going down the highway I heard a knock in my tranny. I got off and realized something was wrong. It knocks in every gear except for 4th and only when I let the clutch out, as long as it's in neutral or the clutch is in it's fine. It sounds like something is bouncing around around and knocks faster the higher the rpms. Any idea what it could be or what I should do?