I have a 04 sentra it has a rattle in the motor what could it be

Kash1980

Sentra

Mr_Shiftright

Could be lots of things--depends on when it happens and under what driving conditions.

Possibilities:

1. If only when cold, on first start-up -- timing chain (which I think your car's engine uses)--this is a light, erratic rattle. Could be a loose chain or a bad chain tensioner. Another possibility is a loose valve lifter, which I think are adjusted with shims on your engine.

2. If the rattle occurs when you press on the accelerator, and it sounds like a chain dragging under the car, this could be "pinging" or "pre-ignition" and that would require your immediate attention, as you might have a bad knock sensor, or perhaps poor quality fuel--did you try to use a lower octane fuel lately or buy some at a funky gas station?

3. Some loose accessory, like alternator bracket or AC compressor bracket.

In any event, have a mechanic put an ear to it, as you don't want to incur further damage.