Belt slipping and power supply making noise

The alternator screws may have been stripped.

Your serpentine belts tension is loose or the belt is going hard. Check the tension on the tensioner pulley and condition of belt.
The belt is slipping on your accessory pulleys when a load is placed on them such as power steering, alternator and clutch fan.

Might be the drive belt slipping on the pulley. The belt that supplies the power from the main motor to the drum sometimes slips at higher speeds and needs the belt tensioner adjusted to tighten the belt. A more expensive reason for the noise is a worn bearing in the main motor.

Remove the end cover.
The tension mechanism will be visible. Loosen the screw, apply some tension, retighten the screw. Quite easy to do,

Watch this videos:

http://www.youtube.com/watch?v=-oeXTKqWECw&feature=related
http://www.youtube.com/watch?v=GPI6dFJCUA4
http://www.fixya.com/support/r10786838-test_procedure_dc_motor
http://www.fixya.com/support/r10724803-measure_voltage_in_transforme_fitness
http://www.youtube.com/watch?v=bF3OyQ3HwfU&feature=related

hi,
There is no gear on the teradmils. Motor is directly couppled to a fly wheel which is a part of the frond roller. FIrst of all oppen the treadmill motor cover and check the belt between the motor and fly wheel . If that belt is loose then this can happened. You will hear a wistling sound when there is load on the treadmill waking belt. If the belt inside is ok the you have to check the waking belt tension. The folloeing video will help you to Tighten the teradmill waking belt.
OK

it could be the tensioner, water pump, alternator, A/C compressor, power steering, or even a really bad serpentine belt. The only way to be sure is to remove the s-belt and spin-check the pulleys and listen for squeaks or grinding bearings.

Lubrication may not be the issue, belt tension could cause the slipping at the end of the unit their is 2 tension bolts. 1/4 turn clock wise on these bolts will increase belt tension, start with 2 quarter turns on each bolt then start unit and proceed to walk on it, see if slipping has stopped. If not repeat procedure only turning the bolt 1 1/4 turn at a time until until proper tension is achieved. If the unit need lubrication then us a tube of clear silicone which you can purchase from Landice,
Call them @ 1-800-526-3423

If the walking belt slips when walked on, first remove the key and UNPLUG THE POWER CORD. Using the hex key, turn both idler roller bolts clockwise, 1/4 of a turn. When the walking belt is correctly tightened, you should be able to lift each edge of the walking belt 2 to 3 in. (5 to 7 cm) off the walking platform. Be careful to keep the walking belt centered. Then, plug in the power cord, insert the key, and carefully walk on the treadmill for a few minutes. Repeat until the walking belt is properly tightened.
If their is still slippage then the drive belt will need to be adjusted.
Find the motor mounts. Many motors in Icon treadmills have a main pivot joint in which a bolt runs the full length of the motor mount. This bolt will require loosening to provide maximum adjustability. Find the set bolt(s) on the motor.
This is typically run through only one side of the motor mount or may be on both sides but it does not run the full length of the mounting. Loosen this bolt but do not remove.

The drive belt must be tensioned by hand. While one person applied increased tension to the drive belt, the other person should tighten the motor set bolt(s) that are described above. Tighten the bolt and test. If the problem is not corrected, if problem persist replace drive belt

You need to tighten/replace your alternator belt as it is either worn or loose.