There are a lot of posts about the whistling coming from the ACE grill work. My ACE has the squire grill work, and when driving in the rain the whistle was a very high pitch noise. Thor has a replacement grill that solves the problem, or makes it better. I called Thor they sent me the replacement type grill, it was not much more than a screen. In stead on removing the old and replacing with the new, I just put the new grill in back of the old. Yes I still get some wind and rain noise but not the high pitch as before.
Retired and never looked back