Re: Harmonic noise coming from engine...
There are some small diameter black metal pipes that enter the firewall at the left side (facing forward). I moved then a little and packed a bit of rubber foam between them to ensure they don't touch anything or each other to avoid any resonances. Perhaps this might help if that's the problem. I like to go over the car to ensure that all wires and hoses are secure and not flopping around against anything. Where it can't be avoided I've used bits of split plastic electrical conduit to keep things separated. The conduit can be got cheaply (in Oz) at Bunnings or Jaycar.
Ordered 9 Nov 2011 - Delivered 3:30pm Friday 13 April 2012
Jeep Grand Cherokee Laredo 3L CRD, Black Forest Green Pearl, Quadra-lift, Off-road Adventure II, Front Recovery Hook, Mopar Tow Bar, Mopar Rock Rails, 150A Projecta Battery Isolator, Tekonsha P3 Brake Controller, Bridgestone D697 265/60R18 LT, Kimberley Kamper Special Edition
MudMap M7 off/on road sat nav, Chief front recovery hooks "chrome", Chief 3mm bash plate, Bluespark pro+boost tuning module