Pete, did you tighten up those rubber nut thingies really tightly, or did you leave enough so that there was a thin layer of rubber between the shield and the mounting points?
I've had no trouble at all with my F-15 (except for some vibration at idle), although admittedly I've only done just over 2,000 km since last May (ie. to work and back on fine days - that's about it).
Scott