Truck Repair: ford f250-funny rattle when shifts from lower gears into high, rattle sound, high pitch

Question
Hello. I am interested in buying a particular f250 2004 v10 (it has extended cab and an eight foot bed). When we went on a test drive, there was a funny high pitch rattle when the truck shifted from first into second (it happened once shifting from second into third). The dealer is insisting that its a loose heat shield. I can see his point because it was a rattle, not a shifting sound, however, he is trying to sell me this truck and I honestly don't know. Therefore, I guess the question is can a heat shield make a rattle sound ONLY when the gears are shifting from low to high?-Thank you- Amanda

Answer
Hello Amanda,
A heat shield can make some strange rattles, at different times.
If he really wants to sell it, why doesn't he fix the heat shield?

If you are the type to slide under a truck, get them to show you the shield, so you can make an informed decision. it should rattle if you smack it with your hand also.
A little prying and bending might also correct it, unless a mount is actually cracked or broken on the shield.
I have also seen stones get trapped between a shield and an exhaust part, and cause noises at certain rpm's also.

That noise during shifting could be from a change in torque allowing things to touch just during that shifting of the engine and transmission on the motor mounts.

Van