Control arms, tie rods, ball joints - I had an issue similar to this, could
not find the noise, until I hit a particularly bad rail crossing.
The metal bracket that holds the sway bar to the frame was cracked,
allowing the bar to bang just a little.
Current DD: 2012 VW Jetta TDI
Newest truck: (11/2011 - 3/2013, Sold!)
2009 Toyota Tacoma, TRD sport 4X4 crewcab
New truck: (December 2010 - October 2011, SOLD!)
2004 Chevy 2500HD, LB7,
bone stock for now Hypertech III, K&N
cold air, Cooper Discoverer HTs, Rhino liner...
Old Truck: (2003 - 2010)
1997 GMC Sierra X/C longbed, 6.5 / 4L80E 240,000 + miles, original IP, 3rd PMD, (now remote mounted Dipaco)
deleted vac pump and home made TM, ceramic pads, Outlaw rims with new Cooper ATRs