Hey everyone. Here is a question that has me stumped. On a '99 expedition (5.4 V8) my heating system is making a strange grinding noise regardless of whether I'm on A/C, panel, defrost, etc. If continues even when I turn the system off. If I do not use it for a few days it goes away. But, as soon as I use it again the noise comes back.

Does anybody have any idea of what this is? It's somewhat of a cross between a gurgling and grinding type noise. Somewhat hard to describe.

If you need more info, let me know.

-Jarrad