growl noise after and during towing
 

So, I have a 2000 4Dr Blazer 4WD. It's on its second rebuilt transmission (seriously). I have a boat that I tow to and from the lake. During towing, I occassionally hear a constant growling/whirring sound. The pitch starts very low at low speed and continues to rise in pitch as speed increases. It doesn't tend to follow the rpms (meaning it continues to rise as the auto-tranny shifts). After towing for the rest of the day, the sound remains. The next day its gone.... Any thoughts? My transmission is still under the warranty from the last rebuild. I'm going to bring it in to get checked out, but wonder if anyone has any thoughts.


Also, I always tow in D3. And drive in D. The noise occurs under both.

transfer case issue maybe? of course im probably way too late and it has probably been dealt with.