I have a 2000 F 150 4.6 litre V-8 Which makes a rumbling noise after a cold start and then only at idle until the engine reaches operating temperature this dos not occure again until the next cold start. Any ideas on what the problem might be?

 

I have the same truck, no answer but giving you a
Bump

 

If the rumbling sound resembles a rattle, sort of, it's likely piston slap. That would be the least worrisome prospect, there are far worse which can be considered. imp