After you have cleaned around the motor, look for any grease fittings, these are usually found on commercial grade units, but yours might have some also.
 
If you don't have a grease gun you can buy a small gun and grease at your local auto parts store for less than $10.00.
 
Check all drive belts for wear, look for cuts and nicks, and replace as needed.  Loosen the walking belt, most treadmills have either a bolt or screw on each side at the rear of the unit. Loosen these, push the rear roller toward the walking deck until the belt is loose enough for you to look underneath.
 
Raise the belt and inspect the underside for wear. If it looks worn or burned you need to replace the belt.
 
Inspect the walking deck for wear, you will be able to tell if it’s worn. If it has little ruts worn into it or bare spots it needs to be either flipped or replaced.
 
 Many treadmills today have walking decks that can be flipped. If your deck is worn flip it, but it is recommended that when you flip the deck you replace the walking belt.
 

To view the information on-line just use the next button at the bottom of each screen.

 

Use this link for the Full Treadmill Report

Treadmill Belts