SHELBY GT 350 Member
Joined: Sep 2010
Location: see user name
Get an automotive stethescope (seen them at Harbor Freight for $5) and start poking around. I agree with the above, could be an exhaust leak since you hear it better by the front wheel, but it could also be resonating from somewhere else. Check the valve covers and engine front cover in particular. A common place for an exhaust leak is where the manifold mates up to the midpipe on the passenger side.
2001 GT Convertible
All the usual bolt-on's /200 I6, C4
And a few Explorers too... 2008 4.0 XLT 4x2, 1996 XLT 5.0 4x2, 2003 Sport Trac XLT 4.0 4x4