Hello out there!
For any of you Thor ACE owners who have been driven nuts by a high-pitch wind noise like me, and you have struggled to figure it out - I have a solution.
I tried everything - went through 4 cans of spray foam sealer, plugging every hole I could find, I looked at windows, taped weep holes, search this forum and the whole dang net for a solution.
The problem is the front grill. That ugly square hole thing that came from the factory. I removed it and did a test drive and bam, all high pitch noise completely gone. Called Thor, they said problem is coming from the half-open squares around the perimeter of the grill. They recommended sealing each hole around the edges and taping over them - did that, still didn't fix it. I'm convinced it is the square openings and the depth of them, causing wind to squeal at high speeds. Here are pics of the old grill and my attempts to seal the partially open holes.
Not pretty, but I tried to do things per Thor instructions.
So here's how I solved it - I purchased a new grill from customcargrills.com and installed it and bam - problem completely solved.
Here are pics of my new quiet grill installed attached.
If you have been going nuts trying to solve this, I hope this helps. That noise was driving me crazy