I had an awful time a few years ago with a terrible growling, whistling, roaring noise in the front of the coach--around 30 -70 MPH.
After extensive trouble shooting with Workhorse and Allison- to no avail- I was ready to call it quits and dump the coach. I eventually found and solved the problem on my own. I removed the grill and the noise disappeared. I then added stiffners to the horizontial fins,repainted and all is well now.
What I didn't know until Bill Morrison came by this past Saturday and we chatted, was that my '02 model Mountain Aire 3778 and his '02 Mountain Aire 3778 had different grills. I couldn't figure out why no one else was having the same problem I had. Look at the pictures below---
My '02 Mountain Aire with slanted, downward horizontial fins-- If you look close you can see the 28,1/8" round stiffners I added- that solved the problem.
Bill Morrisons '02 Mountain Aire with absolute straight horizontial fins-- No noise problems.
The four times I contacted Newmar, in about a 7 month period, I was told they did not know of any problems associated with this noise problem I was having. Later models have the same downward slanted grills as mine except the leading edges of the fins are bent downwards another 20, or so, degrees. It was an expensive lesson for me-- about $2000 for new front wheel bearings, seals and transmission teardown.
Final closure on the problem for me-- I think