Ok, I tried to be systematic about my testing and here is what I found. I have a Thor ACE 30.2. I had the high pitch squeal between 55 and 70mph.
1. Tried tightening engine locks, no sound difference
2. Tried adjusting broken slats on grill, no sound difference
3. Removed grill completely, sound was gone
So I figured out my issue was actually with the grill. So I removed it and added a piece of window screen to the front, attaching with zip ties. When I screwed it back in to my rv, the high pitch squeal was gone! Thank the lord.
Photos below of:
1. Me covering the grill
2. Close up of zip tie attachments
3. What it looks like attached to my rv (hood open for those who don’t know how it opens)
4. A view of inside the engine bay of how the grill attaches to vehicle
My real test will be next week, heading out for 1200 miles.