No, I don't think your springbars need to be modified, and "shock loading" is certainly not an issue at low speed. Unless you are carrying your rock collection, your tongue weight is somewhere in the 500-600 pound range, which is OK for your setup. I don't see any problem, except the BANG when going over a speed bump. Something is wrong there, and you need to find and fix it.
First question - when you say "going over a speed bump", do you mean the moment when the tow vehicle goes over the speed bump, or the moment when the TM goes over the speed bump? If you need to, set up an artificial "speed bump" in your driveway - maybe stack up a couple boards - and drive over it slowly while someone stands beside the speed bump, watching and listening. Figure out what is hitting what, and if it doesn't suggest a fix, take a picture of whatever it is, and get back to us. If it is hitch-related, I don't think it should be ignored.
Again if it is hitch-related, the question is, is it something about your hitch adjustment that is making the noise? In other words, is something hitting something that it shouldn't? Or, as Dick suggested, is it something entirely unrelated to the hitch, like the steps? If you have a second person watch the action, you will quickly find the answer.
If it is hitch-related, my guess - and it is only that - is that your springbar tips are too high, and when the back of the truck rises up on the speed bump, the tips contact the underside of the trailer A-frame. If this turns out to be the case, a simple adjustment will fix it. As gmferg asked, how many chain links do you have between the springbar tips and the lift hook? Somewhere on the order of 5-6 is proper, and 2 or 3 is too few. There are people on this board who are very experienced and willing to help. Get back to us.
But the more I think about it, the more I am with Dick - it is not hitch-related.
Bill
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