Well, it started probably 5-6 months ago, it was faint and bareable. More recently, the rattling is starting to get very aggravating and it gets louder with speed. It only makes the noise while maintaining a constant speed. Durring decel and accel the noise doesn't exist, unless at wot. When I try and hold the shifter steady with my hand the noise still continues.

Any ideas on what this could be and how I can fix it?