Weird Noises

I have a 91 ford explorer and i boughtr it used since i have owned it i have put about 400 KM on it and when i first bought it it mad a weird sound but it cut out after a couople of seconds. Now the sound stays on for like 15 minutes with the ignition on does anyone know what the problem is and what can be done about it?

Also, A friend has told me that it is my fuel pump but when the ignition is off the pup still runs this time it did not shut off i had to disconect the battery post please help!!!!!