anyone heard these sounds....99 silverado

[hihosilveraway]

here goes, i tried searching, but really don't know what to search for. i have a 99 silverado with the 5.3 automatic tranny. the first noise is sorta of like a rattle under throttle at around 2500-3000 rpms. it is more prominent in the summertime when the air is on and the engine is working harder, but it is heard in the winter too, sounds like it is coming from behind the dash on the pass. side though.

 

another only happens when people are sitting in the back seat, ext. cab. usually when i am decellerating around 15-20 mph. its a really nasty klunking coming from underneath near the pass. side. up front. i never notice it when its only me or someone in the front riding.

 

hope you guys can help me out, i'm new to the forums.

 

thanks

jonathan

[XR Man]

The first sounds like detonation, try a higher octane gas. The second is the rear seat upper mount--search for a TSB on it.

[Tucson_02Silverado]

Is the sound only happening from 30 and below?

 

A little worse when making a turn? Right turn from light?

 

Are you sure it doesn't make any noise with just yourself? Windows closed?

 

Does the sound seem like it is coming from right in front of the passenger seat at about dash height?

 

At some other times it seems like it is coming from the suspension?

 

Stock air box?

In my particular case, my air box had one of the "slide lock" foot broken on the bottom. The air box rattled just like metal on metal. The sound was almost like that of loose suspension. The sound would be completely gone by 30mph. I found the broken piece lying just under the mounting plate. It was broken in such a way that I was able to drill in the middle of and reattach it with small bolt.