I fixed my noisy soccer ball motor for 5$ and it is a job you can do in 5 minutes.
I had purchased a replacement motor from Marco supplies, and to be honest it was even louder than the old one... MUCH louder. It sounded like a remote control electric car was 5 inches from my ear every time it turned on... I wonder what their return policy is... If I can't send it back it's going to go up on the classified section with an honest description.
In any case, before I reinstalled the old one, I took it apart and saw that there was 25 years of gunk in there. After some research, I cleaned the motor with a paper towel and squirted in some Lithium Grease (5$ at Home Depot in the Automotive Section) and hooked it back up. It is MUCH quieter. You can still hear it, but it is not nearly as loud, spins up faster, and continues to spin a little even after the motor stops sometimes.
If you wanted to do this yourself, you can do it without having to solder anything and by only removing 2 screws. If you look at the motor, it separates from the gearbox with 2 flathead screws. If you remove those, the motor will pop out leaving the gearbox. As you can see from my photo it was filthy. I gently wiped it with a paper towel and squirted in the lithium grease. Make sure you do not lose the little black O ring. The whole process should take maybe 5 minutes.
I also installed a new soccer ball from Marco. It is fantastic and very grippy. It grabs and throws the ball much better than the old one, and these can be installed simply with just a phillips head screw driver.
After the success I had here I went ahead and squirted some lithium grease in the goalie motor using the same process, but it didn't seem to make a difference.
I am slowly switching out the bulbs in the machine with LEDs and it makes a huge difference. I'll post pics when it's done. I have some new connectors coming in that I will be using to fix some electrical connectors that should bring up my back box light and stadium light in the next week. This should bring my machine up to about 98%. Having a blast fixing old stuff. Great game. "They can't seem to get control of the ball"!
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Added over 3 years ago:
EDIT: Before you do this, skip ahead to post 4491. There is a better way of quieting the motor.