2010 X5 35d loud exhaust noise at 60mph

[bracoX5d]

I have a 2010 X5 35d with 56k miles. Recently it started making a really loud booming exhaust noise right at 60 MPH; well I think it's exhaust anyway. It sounds similar to when you suddenly lift off the throttle when accelerating but much louder. The strange part is that it is right at 60MPH, if I go a little above or a little below it goes away. Anyone else have this problem? Any clues as to what might be going on?

[ard]

All windows and sunroof closed?

[bracoX5d]

Yes, all windows and sunroof are closed.

[dubsesd]

Are you sure it's not turbo spool as you accelerate?

[Price]

Check if have any of the protective panels underneath came loose.

[seattle]

"booming noise".. um.. Sonic boom at 60 mph? ))
It would help better to record the sound and post here..

[bracoX5d]

I don't think it's turbo spool as it remains constant at 60 mph and goes away if I go up or down. I'll try to record it tonight and post it here. I'll check the panels too, I didn't think of that.

[seattle]

Can you try 60mph in various gears? Just to play with RPM range and gears.