I am hearing a faint whistling sound which seems to be coming from behind the guage cluster on my 2005 Duramax. I lifted the hood but could not hear the same noise. The noise is faint, intermittent, and can best be heard at idle while the vehicle is stopped. Sometimes it sounds like a whistle and sometimes it sounds like the hissing of a vacuum hose that is not connected. It seems to happen more when the engine is warm. I put my ear up to the guage cluster and it definately sounds like where it is coming from. I'm going to be scheduling an appointment at the dealer, but I would like to know if any of the techs on this site have any ideas or have heard similar noises.

I know it is difficult to diagnose a noise without hearing it, but does anyone have any ideas? I am a new diesel owner and I'm still getting used to the sound of this truck.

Thanks

Check the heat shield on the firewall and make sure it is not contacting the downpipe heatshield bolts. Also, if it only happens with your foot on the brake, it is the hydroboost, and it is normal for it to make a slight hissing noise.

Thanks for the quick response. I will go take a look.