Hey guys, I wanted to ask you guys, since almost everyone is here, that are very knowledgeable of this sort of stuff.

https://mustangforums.com/m_4097847/tm.htm

Mods, if you can let this one slide for a little while, I inititally posted in the tech section. Thanks again!

 

From your description, it is invariably the exhaust mount. Go drive it again and see whether it is only at 35mph, or whether it is in all gears at a particular rpm.