Replaced the timing belt on an 02 niss xterra and starts like a champ but has a noise or knock now any suggestions??

Common Car Noises and Their Likely Causes Noise More Details Likely Cause Fixing It Clicking noise while turning Starts faint, gradually becomes more noticeable until very loud Failed outer CV joint (constant velocity joint) due to torn boot (most likely) or old age Replace either the whole axle assembly (recommended) or the outer CV joint Water pump noises Difficult to diagnose because of water pump's location Noise usually caused by damage to the bearings in failed water pump Only cure is replacing it. If possible do it at the same time as a timing belt replacement to cut down on labor costs Squeak or squeal from an engine belt Loud, high-pitched squeak or squeal Belts either need adjustment or replacing If belts only squeak when damp, they probably just need adjustment. If they squeak constantly, they probably need to be replaced Exhaust heat shield noises Rattle that you hear when car is idling Damaged heat shield Replace heat shield

I just replaced this on 02 xterra 3.3 L V6. The knock sensor is in the center of the engine block below the lower intake manifold. Its a lot of work but it wasnt too hard just took time. Getting some of the hoses off in rear of motor was hardest part. But you need to remove upper and lower intake manifold and you will see it.

The only cure to fix squeaking belts, is to replace with the new one. When the belts start squeaking noise, then it is the time to check the status of the timing belt or chain, depending on the size of the engine.
The 2000-2004 Nissan Xterra was offered with the choice of 2.4L 4-cylinder or 3.3L V6 engine.
The 2.4-liter 4-cylinder DOHC engine was a pretty good reliable engine, but for this truck, it was underpowered. This engine has a long-lasting timing chain - there is no timing belt to replace.
The 3.3-liter V6 SOHC was also a bit slow on pick-up, but for daily use, it was pretty good, durable, simple engine. This engine has a timing belt that needs to be replaced at recommended intervals. The SE model offered a supercharged version of the same engine with more power.
To get more information, please read my tip :
When should I change the timing belt on my car?
http://www.fixya.com/cars/r6481199-when_change_timing_belt_car

you would want to verify, but most likely 90,000 to 100,000 miles.

These Nissans are giving trouble with the tensioner pully. When they retightened it after replacing your belt it probably made it start squealing. More tension than it had before. Get it checked. If it locks up it will damage the engine. I have heard of the dealer fixing some lower mileage ones for free.

Was the the issue there before the new timing belt. It may be off a couple teeth. Do you have the correct type sparks plugs and the correct 02 sensors or some universal,splice in ones. When warmed up it goes into closed loop and the 02 sensors take over part of the fuel stratagy.

I would ask for all the codes the Xterra is setting. Also, does your odometer stop working ever?

If it's the water pump there should be water leaking, if it's the steering pump the noise  would change as you turn the steering wheel left to right. If it's constant, it could be just old belt and bad idler and tension pully. Start buy praying a little water to the belt while the engine is running and if the noise goes away, the belt is in time to be chaged. If the noise is still there, then most likly it's the ilder bering or tension bearing. Good luck

Balance the tensioner and that should get rid of the rattle.

I suggest you begin by charging and testing the battery, your description indicates it is discharged.

Why it is discharged remains to be seen - you need to check the alternator drive belt and the alternator charging.