When pulling my 32 ft. Montana with my '05 DMax I hear an occasional but consistent roaring that I assume is the fan clutch kicking in for a brief period of extra cooling. The temp gauge doesn't show any movement, but for about a minute or a little longer the roaring continues. When not pulling a load I don't hear anything. Am I correct in assuming this is what I think I'm hearing? It's just noisy and a little worrisome, too. Any comments out there?