Don't just check where the axle housing bolts to the bracket (although that's the most common place they come loose). Also check where the brackets attach to the frame. They attach there using a rubber bushing to allow some 'give'. If that bushing has been damaged, it could allow the axle to move in relation to the exhaust.
Also, any time that you've had it in 4L, toss a little terra-firma in reverse once you have it back in TOD. It may not help ... but it don't hurt either. Blue haired 4 wheelers learnt to do that back in the day to ensure that the transfer case fully dis-engages.