(2000 4.0 XJ w 155000 miles)
After a long drive today I could hear a distinctive hum coming from the cargo area - something I've never heard over the past three years I've had my XJ.
I found that when I pushed down above the fuel pump in the cargo area the humming stops - could it be that something is simply loose?
I'm assuming its more than likely the end of my fuel pump? Is there any way to test it? How long do I have approximately?

Thanks!

 

The key to fuel pump noise is "if it is increasing". Increasing fuel pump noise is your cue to replace the entire "fuel pump assembly". Knowing how long it will last is impossible to estimate.

Do you know how many miles are on this fuel pump? I'm assuming it is not the original.

 

If it stops when pushing on the floor, yes. Something sounds loose. Crawl underneath and look for anything touching the tank and cargo floor. Could be a metal brace under the floor, wiring, or a bracket.