Programmer on a Vortec 5300 (5.3L)

I have a '99 Silverado Z71 with the Vortec 5300 - awesome engine. I have never had any problems with my truck and has served me faithfully from the day I bought it at roughly 144,000 miles until today 168,000. I have put a flowmaster exhaust system on there and have swapped the stock airfilter for a K&N filter. This past summer I bought a Hypertech Power II Programmer for my truck with dual fuel technology. I programmed my truck to run best on 87 octane, for the transmission to have harder shifts to extend trans life, and I reset the governor to 128 mph (my tires' max speed rating). Ever since I reprogrammed my truck there has been a slight rattle behind the driver side dash during light acceleration. It does not rattle while coasting, harder acceleration, or while cruise control is on. The truck still runs great and I notice an increase in power, but should I be worried about this sound?

Edited December 3, 200619 yr by VMIZ71