I am having a noise too, always been there since i got the truck but getting louder. Mine is more of a grinding noise or that of a pulley being loose, but I replaced the idler pulley as it was wobbly but no fix. I guess I will have to try removing the belts and see if it goes away. But I got to thinking as I stuck my head in close to listen and it sounds like its behind the timing belt cover. I see that there is two smaller idler pulleys inside for the timing belt itself on parts diagrams and wonder if one of those may be bad. Because it does sound like a bearing that is going out and grinding. Anyone ever heard of those going bad and making that grinding noise? It almost sounds like a chain slapping noise too if that helps describe it better, even though it couldnt be that because its a belt not a chain... But thats what it sounds like..
Oh and the temp does not affect it at all.