I agree with the folks that are betting on timing-- think smooth acceleration and sudden stops rather than power and brute strength. And as Jim (wjc) says, if you're hearing crack the whip sounds it's probably because you're not waiting long enough for the the backcast to straighten out.
Since you're near St Louis you might want to check out Tom Hargrove's shop THargroveInc
In addition to being a pretty neat place, Craig Stephens teaches fly casting classes, and you might be able to get a few pointers. When i think of classic fly shops, this is the kind of shop i think of, down to the cast iron stove. I used to pop in whenever I went to St Louis on business. ( edit---I just saw Oregonsteel's post about feather craft's free casting lessons-- go for it-- it's another great shop and great folks.)
I always recommend joining up with a local chapter of Trout Unlimited or a club affiliated with the Federation of Fly Fishers, so i'll throw that idea out too. In addition to group trips to local waters, informative meetings etc, they often have formal or informal casting clinics, tying classes etc. It's a great way to knock years off the learning curve.
You might want to check out these guys that are based in St Louis- it's a club affiliated with the Federation of Fly Fishers:
Ozark Fly Fishers
You can also do searches here to see if there are other groups closer to you:
Council/Chapter Contacts | Trout Unlimited - Conserving coldwater fisheries
FFF affiliated clubs:
Locate a Club
You can also do a search for certified casting instructors on the FFF site (click on the "Education" tab for a drop down menu, then click on "Find a Certified Instructor") Rates will vary for 1 on 1 instruction, typically from 25 to 45 an hour.
Good luck and keep us posted!