I got an email from a customer the other day asking if I had any suggestions to a noise problem. It was a strange issue, because it only happened when she treadled with both feet. When she would switch to single foot treadling, it wouldn't knock. What was really bad, was it seemed to be getting worse.
The answer to problem lays in the mechanics of the wheel. When a person treadles the style of wheel SpinOltuion makes, there is a bearing point on the wheel, off of center that is driven by a slotted plate at the end of the pitman. This photo shows the plate removed

from the pitman arm. The bearing in the center of this picture runs up and down the sides of the slot as you treadle. This is what drives the wheel. This is also a wear point. The is why we made it removable. The noise comes from the bearing slapping the opposite side of the grove when you push with the other foot. If you only treadle with one foot, the bearing stays against the one side. This noise issue is one of wear management. You want the bearing to run free so the slot needs to be loose, however, if it becomes to loose, then it starts making noise.
An easy fix for reducing the noise is as follows. Please keep in mind that the bearing needs to have a little clearance so it can roll freely.
Step 1: Grab the treadle, with both hands near the pivot point, and pull gently away from the body of the wheel.

This will separate the pitman from the wheel.
Step 2: Gently push the pitman plate back towards the wheel, removing it from the pitman. The easiest way is to grab the pitman and use your thumbs to press the plate off. The Plate is held on by 3 metal dowels.

Step 3: Coat the inside of the slot with either Elmer's glue or fingernail polish. In the picture below, I used my wifes hard as nails clear fingernail polish. Finger nail polish is nice to use since there is a brush and is hard when it dries. However Elmer's glue works just as good. Let this dry off of the pitman or it might dry to the pitman, and you will have hell trying to get it off the next time.

Step 4: Once the polish or glue has dried, reverse the order to reassemble. Some things to make sure of, the metal dowels are not protruding through the plate as it will rub against the wheel and make a mess of things. Also, make sure the bearing is inside the plate slot. Once reassembled, give it a spin. Your wheel should be noticeable quieter. If the plate is to worn out, it can always be replaced.
Good Spinning
Mike