[Dark Taco]

First thing that comes to mind........check your mud flap if you haven't taken it off already.

 

[05Moose]

x2

http://www.toyotanation.com/forum/showthread.php?t=333192

 

[ttetaylor]

Problem SOLVED.....Thanks Dark Taco. The mud flap looked fine but was cracked in the middle along the seam. 45 to 55mph was the wind speed needed to bend the flap and make the poping noise. I removed both flaps on the front and no more noise....thanks again.