Rattle from passenger side dash only when brake pedal pressed

[DCadigan]

I have a very loud rattle coming from the passenger dash/firewall area. It only occurs on hot days and when the brake pedal is depressed. Soon as I let off pedal it goes away or if I shift trans to neutral. It drives me crazy sitting in traffic or at a stop light.

 

[Bob4x4]

If you can reproduce the noise that easily,have an assistant track down the source while you are creating it.

 

[DCadigan]

Tried that already... I think it is coming from under the hood... just can't tell because of the engine noise. I even had the dealer look at it. The mechanic wrote it up as "unplugged 12v splitter plug in outlet and noise stopped. " Got truck back and 2 days later without the splitter plugged still rattling. I guess my next plan is to let the rattle start and just drive straight to the dealer.

 

[AEdelheit]

Ive seen the transmission dipstick hit the firewall, worth checking.