Just a question: what map is this? Maybe the treasure location is on a small island in the sea. Or in the middle of the desert, and what you perceive as white noise is simply a scenery-less expanse of land?

It's one of the fan made maps with the extended features... "Surf 'N Turf". but I don't think that's the problem. It does sort of look like ocean background, but there are little pixilated rectangles in a regular pattern throughout. I'd attach an image, but the game is on a different computer and I don't think it's worth trying to take a screen capture and moving the file over to this machine... I was hoping someone would recognize the problem. It's a problem I've seen before. It's hard to search for answers on the net because there are so many editions of HOMM and result lists are inundated with false hits for heroes 3, 4 and etc. and other kinds of map and editor problems. Thanks for brainstorming with me though.

Sorry then. I don't believe I ever came across this problem before.

Maybe you could link to the map and I can check if the same problem happens in my game? Googling I found a reference or two to the map, but not a working download link.

I started another new game and the behavior of the map is good again. The only difference between this game and the previous one is that I started from a new launch of the game. The game that had the problem I started after completing a game without exiting to the desktop first. There is a button on the menu displayed after entering a high score that allows one to begin a new game. Perhaps if I avoid this button I will avoid the problem in the future.