My 2000 Lincoln Ls makes grinding noise underneath car

It's not a typical box shaped tank. It looks more like a butterfly. Look for a skid plate over the tank which has two metal straps holding it up.

Hi Nancy:
The first thing that I would be suspicious of would be the starter. What happens when you try to start the car? Does the starter turn over? Is there a clicking noise? Did the car run fine after starting with the grinding noise? If it did, then the grinding was probably associated with the starter. If you pull the starter and the little gear on the pointy end is all chewed up you'll be on your way to solving the problem. If you're lucky, a rebuilt starter will probably be most cost effective and hopefully (usually) the ring gear will be OK.
Hope this helps.

the grinding noise is from the steering pump going into overload and the pressure relief valve is working. If you have recently worked on the pump or steering check that the hydraulic lines have correctly installed It appears that when turning right the steering is trying to turn left.

it may have jumped time..need to take it in and see..

Bad News, your rear end needs rebuilt.

YOUR TIMING CHAIN GUIDE MAY BE BAD CAUSING YOUR CHAIN TO MAKE NOISE,THE WAY TO KNOW FOR SURE IS TO REMOVE COVER AND SEE,HERE'S A GUIDE ON HOW TO DO.http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?fromSearchPage=true&pageId=0996b43f802e863e&partName=Timing+Chain+Cover%2C+Chain%2C+Sprockets%2C+%26+Seal+2&partId=0996b43f802e863e

until someone inspects it its anyone guess.

you have to put your car on jackstands crawl under it to see if it is moving feel the cadillac converter moving or not

If it is a whining noise and not a metallic grinding (such as a bearing noise) and the noise seems to change with a light change in load; IE- louder with maintaining speed on slight incline versus quiter on deceleration, then you are likely to be hearing a worn ring and pinion gear set. Changing the fluid will not affect this type of noise and if the old fluid was free of metallic debris, then you have time on your side to prepare for replacement of the ring and pinion. A great deal of customers are opting for a used differential which is usually a bit less expensive than rebuilding the one you have.

I would have to guess it is your rear u-joint is going to have to be replaced. Or your pinion in the rear end is loose or faulty.