I'll bring a 15 mm with me then and give each side a turn to see if that cures it.
You will usually need more than one wrench. It explains how in the manual, loosen the rear axle bolts (wrench on each side), put a 10 pound weight on the track in the middle 16 inches in front the center of the rear axle. Measure distance between the track and the bottom of the hyfax 16 inches from the center of the rear axle. Should be 3/8 to 1/2 inch. After your done adjust the track so it runs straight, if you measure from the hyfax to the outside of the track I think you get around 2 and 7/16 inches.
Like said don't forget to check the drive chain tensioner, it's also in the manual.