Try to soften the click using the methods suggested (putting a piece of sticky tack (blutack) or tape over it also helps).
For me I taught CASUAL loose leash walking like this:
1. I imagine a fairly large square right next to my left leg (and right leg if you don't mind your dog walking on the right side too).
2. Every time the pup walks in that square (basically falling into place by my side), I click. Click EVERY TIME and the pup doesn't have to be exactly in the square in the beginning either (start easy first - say front paws or just back paws). Feed the treat WHILE WALKING. For this reason, keep your treats small and soft (bits of ham, cheese, steamed chicken, egg work very well).
3. Every time the pup looks at me, I click also and feed while walking.
I did this with Romeo (instead of yanking the leash or standing still then moving when he stops, or walking in the opposite direction of where he's pulling, ALL of which I tried to no avail) and by our 3rd walk he's gotten it and walked by my side for the majority of the way and at times nearly tripped me because he wanted to get so darn close to my legs! Once he's doing it very well and when he was slightly older, I transitioned food treats to life rewards. I click and send him to "go sniff" a tree or pole or whatever. He will work for that and finds sniffing and marking a tree very rewarding. I don't bring treats out anymore!
I say "Casual" loose leash walking because when we're on our daily walks, I really don't care if he's not heeling all the way. I don't mind if he wants to stop and sniff things or if he wanders abit further from my side so long as he doesn't drag me there. And I also don't care much if he walks on my right or left. We're just walking anyway, not in a competition!