Truck starts but makes a noise like when u turn the key on in an already running vehicle

Why would you try to start the vehicle if it is already running?

It should stay running once you put the key in the ignition and turn it on. DO NOT TURN THE KEY TO THE START POSITION. The vehicle is already started!

I'm not sure I understand this question. If you don't use your remote start you should be able to start your vehicle with the key. If you use your remote to start the vehicle, all you need to do is put the key in the ignition and turn it to run (don't try to start an already started vehicle). some vehicles require you to put your foot on the brake as you turn the key. Now your car is running off as though it were starting with the key in the first place.

Is this chevy vehicle?? Some starters need shims when installed to prevent this type of noise when starting vehicle. If your starter had shims, put it back on nee starter..

What happens is that you tried to engage the starter gear into the flywheel. It IS possible to do damage with this act, but rarely occurs. Yes, the noise is horrific. That tends to prevent repeat performances. If the vehicle starts normally, don't sweat this issue.

The ignition switch is not reading the chip in the key, Triggering the anti-theft mode in the ECU.

In order to program them yourself you will need 2 existing keys that are already programed to the vehicle. Step 1: Put the first key that starts it in the ignition and turn it to the run position then back to off and remove it. Step 2: Within 10 seconds repeat Step 1 with the second key that is programmed. Step 3: Within 10 seconds repeat Step 1 with the first new key and so on until you are on the last new key. Step 4: For the final key you will put it into the ignition and start the vehicle. The vehicle should start and all the keys should be programmed. Test out each key to make sure it starts the vehicle. If you don't have 2 existing keys you will have to take it to a Ford dealer and have them programmed. Also I'm not sure what the max amount of keys that can be programmed to a 98 Explorer is but I think its between 4 and 8.

the metal drive plate for the torque converter ??? possibly

Try to do the crank relearn:
Ensure that your battery is fully charged before attempting the relearn procedure. Do not leave any battery charger or jumper cables attached to the battery. Close the hood completely. Some applications require that the doors remain closed during the procedure.
96-99 S10
1. Rotate the key to the start position to attempt to start the vehicle (the vehicle will not start).
Allow the key to return to the all position (same as if the vehicle would have started). The theft system light will flash (or stay lit) on the dash for approximately 10 minutes.
2. When the theft system telltale stops flashing (or turns oft) turn the key to the off position for 5 seconds and then attempt tostart the vehicle. The vehicle should start on this cycle.
3. Once the vehicle is running, the password relearn is complete.

00 + S10
1. Rotate the key to the start position to attempt to start the vehicle (the vehicle will not start). Allow the key to return to the on position. (same as if the vehicle would have started)
2. The theft system light will flash (or stay lit) on the dash for approximately 10 minutes.
3. When the theft system telltale stops flashing (or turns off) turn the key to the off position for 5 seconds and then attempt to start the vehicle.
4. Repeat steps 1 through 3 two more times for a total of 3 cycles/30 minutes.
5. On the next cycle of turning the ignition key from off to crank the vehicle should start
6. Once the vehicle is running, the password is learned and this completes the cycle.
7. Clear any DTC's with a scan tool if necessary. DTC history will be cleared after 100 ignition cycles.
Thank you for using fixya and keep me posted, be glad to help you get your jimmy running 100%

Only if the engine is running,will the loose belt cause a noise in the engine,if it is a grinding noise,the starter drive,may be sliding into the flywheel.