I have an odd problem. I noticed yesterday my quest shuddered (more of a motion rather than any sort of noise). Think of someone coughing repeatedly and the jerking that it involves-that's the best way I can describe it. It wasn't doing this violently, but to the point I immediately noticed it. It does this at about 25-45 mph ONLY when I push the accelerator, never otherwise. This is the first van I have ever owned, so this is all foreign waters to me. I've only owned Japanese compacts before now. So, any ideas what on Earth this may be?