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PostPosted: Fri Feb 12, 2016 10:27 pm 
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Joined: Mon May 19, 2008 10:30 pm
Posts: 8680
Location: Grand Rapids, Michigan
Year and Trim: 2014 Cadillac XTS Vsport.
Author - ddalder


Rear Shelf Rattle Abatement - 2000+ Bonneville

I’ve compiled some information that may help in tracking down and resolving rattles and vibrations in the rear shelf area. It’s surprising how many items I located that did, or at least can contribute to the problem. I’m not going to cover how to remove the rear seat so if you’re not sure, please ask or reference a service manual.

Here are some of the tools and supplies I used.

This CD is used by GM dealers to help identify where problems exist. There are tracks that play sounds of specific frequencies for woofers/sub-woofers, midrange and tweeter speakers. There are also both fast and slow sweeping range tracks along with a silent track for locating unwanted hum or buzzing. Playing the low-frequency track on repeat helped me to probe all areas without interruption until I was satisfied each problem was identified.

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A 10mm flex-head, ratcheting wrench is imperative to remove the two bolts near the rear glass.

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Closed cell foam in 12” wide rolls, adhesive on one side, 1/16”, 1/8” and 3/16”.

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A very sharp utility knife, heat gun and isopropyl alcohol (or similar to remove old tape adhesive) are necessary.

GM refers to the plastic assembly mounted in the rear as an “Electrical Carrier” so I’ll continue with this reference. Once you have the rear seat and rear shelf trim (carpeted rear cover w/grilles) removed you can see the carrier is held in place by 7 bolts (10mm head). Seatbelts are clear of this assembly and you will not need to remove the retractors from the car. There is a LeverLock connector on the driver’s side that you will need to unplug. Pinch the tabs and fold the lever back to separate.

The biggest challenge to removing the carrier is the two bolts at the base of the rear glass. These are easy to access with the wrench (above) until they are most of the way out and clearance is reduced to almost zero. They thread into speed nuts attached to sheet metal tabs under the electrical carrier. Climb into the trunk and pull the tab slightly downward. This will give you a little more clearance to completely remove the bolts.

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With the carrier out you will want to first ensure the speakers are not loose. Check that the fasteners are tight but don’t go overboard or you may strip the holes.

This picture shows where GM applied foam tape along the two sides. The area is actually quite wide but the tape is narrow in comparison. Since the tape wasn’t very thick either, it compressed easily when the bolts were tightened. This narrowed the clearance between the carrier and the body where no tape was applied. This was by far the source of my worst rattle.

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Using 3/16” foam I matched the outline of carrier to body area exactly. I also replaced the tape across the rear vertical surface of the carrier with 1/2 inch by 1/2 inch closed cell foam tape.

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A tab on the rear edge of the carrier also had three small strips of very thin foam tape. I replaced this with 1/8” foam cut to the full lower surface of the tab. I honestly do know if this was a source or not but since GM installed tape, I assumed they had reason to believe it should be there.

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The Remote Control Door Lock Receiver and Electronic Compass Module both vibrated when I wiggled them. The RCDLR has a spring metal tab on the back and the compass has a wide piece of tape that is intended to prevent movement. Neither method works well so I applied a 1/16” piece of foam padding to the carrier behind the modules.

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Lastly with the carrier itself, the wiring harness should be examined. When I first checked the retainers that hold the harness in place they seemed tight. With the CD playing I was surprised to find some retainers did vibrate. GM uses small while foam donuts on some connector retainers to prevent vibration. At least this is my assumption since many have been located in areas where providing a seal is not necessary.

I had several of these from old wiring harnesses on my shelf so I put one on each push-in retainer. They worked very well and you’ll notice later in the thread I also used them in the ‘C’ pillars.

With the retainers taken care of, there were also areas where the harness was vibrating against the carrier. You can either isolate the carrier with some foam (or other) insulation of make sure the harness has enough clearance.

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The rear shelf trim was vibrating against the speakers and the area behind the top of the seat back and body. This picture shows how I’ve added foam tape around the speaker grilles and the grille retaining tabs along with the area between the seat back and body. The plastic cover assemblies for the LATCH system can also rattle so check those. Mine were a little loose fitting into the rear shelf trim so I added a little foam under the retaining tabs.

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The ‘C’ pillar trim (GM calls them a sail panel) can rattle if not secured properly or if the wiring and sun roof drains behind the panels is not secure. I have not added a photo of the trim itself but look closely at the two yellow push-in retainers that secure them in place. I typically replace these every time I remove the panel because they just don’t have the same grip when re-used. Problem is, these are also quite expensive. This picture shows the white foam I placed on the connector retainers to improve fitment.

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Last in my quest to be rattle free was to check fitment of the trim panel in the trunk covering the back of the rear seat. The design of this varies depending on model year so I can’t offer advice that covers all scenarios. Mine is held in place by a press-on style speed nut and magnets. Sometimes these magnets separate from the cover and require reattachment with some type of adhesive. In any event, consider this trim as a possibility as well.

_________________
*Gone, but not forgotten* - Black 2000 SSEi, HIR Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, 180 degree thermostat, HS 1.9 rockers, LSx yellow springs, Intense FWI, PCM, shift kit, push rods, and 3.4 Pulley. ZZP Power Log.


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