Mike: I completely know where you are coming from. My one GSD is the same way. Where we live people love to shoot off firecrakers/fireworks a lot (don't ask me why, they are an odd bunch out here and celebrate everything) and my dog hates it. Goes into some kind of avoidance and acts like a baby. He hides, runs away, poops a lot, does not want to go outside, sticks by my side like he is sick, paces, hides under table......etc.
And its not just the fireworks; also thunder and loud banging like you mentioned.
His wussy behaviour used to annoy me to no end. I tried giving him food, playing with him, walks, acting like it was so great, making loud noises, playing thunder noises quietly in the house. You name it, I did it.
In the end, nothing worked. I just accepted that he has weak nerves (and I'm not saying your dog has weak nerves, I just know that mine has) and ignore his wussy behaviour and when he gets too freaked out (thunder), I just put him nicely in his crate with a good bone and turn up the stereo.
I wish that he was brave like my other dog, nothing bothers her, but what can you do?

OK just an update to finish off this thread...

Yesterday morning I got woken up at 5am by a wet dog nose in my face and whining noises. I took him out, he pooped for the first time in over 24 hours, it was a yucky mushy poop. He pooped 5 times throughout the day and he was a little lethargic on Weds night, laying around, not doing much of anything.

Today he's back in full force. I heard construction noises again, I watched Cujo outta the corner of my eye to see what he was gonna do, he stood in the middle of the room staring out the window, then he heard it again, he ran at the window barking at full force, I smiled <img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> HUGE improvement! He's back to his old self again, I guess he was a lil sick n it was affecting his behavior, because that noise was a surefire "run and hide under the desk" noise 3 days ago! So I took him out to the construction area again, they weren't doing much of anything, there were some occasional not so loud banging sounds and lotsa construction machinery noises, lotsa trucks passing us on the road, lotsa road noise, he was perfectly content jumping over the fence back n forth, running around the grass chasing moths, doing some obedience with me, almost completely ignoring the construction noises.

He hasn't had another encounter with the dump trucks, but his overall behavior is so drastically improved now that I'm sure dump trucks will be a non-issue too.

My dog isn't the most fearless dog out there, but I've never known him to be the bundle of nerves he's been the last few days! I had considered that it may be a medical reason for his behavior but it didn't seem likely to me so I kinda dismissed it.