corradoMR2

Some recent posts on the NX's sound system and speaker upgrades got me thinking about how to reduce the unpleasant car vibrations generated by the sub in the rear hatch, at a minimal cost and effort. This is in addition to buttoning down the license plate and placing rubber or felt as a common fix posted in many forums and threads.

I used two 454g cans of med-high expansion polyurethane foam (i.e Great Stuff, Mono, etc.) to fill about 2/3rds of the door cavity while avoiding the door latch mechanism, the rear camera module, and the sub.

I used fabric tape (hockey tape) along the hatch's interior trim to minimize plastic-on-plastic or plastic-on-metal vibrations.

Result - with volume cranked, significantly reduced rear exterior vibrations. As well, no interior vibrations at rear and to my ears, a "cleaner" slightly louder and deeper bass.

My usual common sense disclaimer that I nor CL is responsible for any damage incurred in doing this DIY. With this out of the way, see video below and hope this helps.

mrsinsyder

Posting to do this weekend.

corradoMR2

Great, post your results!

tresmith00

Corrado - you think I can get the same or better results with sound damping sheets like dynamat?

corradoMR2

^^^ +1.

The thing is, the plastic panel is clipped on with many clips (at least 20) from my recollection (seen through the hole when you remove the plastic bottom covers) and if one's willing to replace some of those clips which will likely get damaged, the panel can be removed. But, to get into the metal door cavity, the only large enough hole is from the sub making it a difficult install for a Dynamat across the entire cavity door, IMO.

tresmith00

maaan, I'm all thumbs. I was asking but I'm going to take it to a pro when I'm ready. lol

mrsinsyder

I tend to agree.

Amazon prime is being slow, and my foam will arrive Monday. Hope it helps.

computerwi

@Pinhead, that is my same concern. What if you need access in there sometime? Especially on a lease, I wouldn't want to do anything permanent.

Now that the colder weather is here in Canada, the rattling is definitely getting worse. I'm finding the loudest rattling in the mornings and quieter by the time I get to the office after driving for 30 mins after the vehicle has warmed up inside.

mrsinsyder

Finally got around to spraying the foam in, and it seems to have made a huge difference thus far, with no adverse effects. Thanks corrado!

corradoMR2

Great to hear and validate the fix!

NickTee

For those not wanting to use the foam, which is honestly a terrible idea to begin with, you can always buy denim insulation or fiberglass insulation and stuff it into the cavity. This will achieve the same filling effect without introducing the mess of Great Stuff. It's significantly easier to control and it can be taken out as desired. It will also have better sound absorption properties compared to Great Stuff. The easiest way to use it would be to remove the panel and lay it in sheets, but making an access hole and shoving it in will also work if you feel nervous about removing the panel. It'll just be more work.

The reason I say the foam is terrible is because it's a semi-permanent "fix" that makes a gigantic mess, and because it relies on air to solidify, it takes a long time for it to fully harden when used in large quantities. This is why two-part foams are typically used for cavities, again a semi-permanent fix, because it's a chemical reaction that won't leave certain parts unhardened like Great Stuff will. And, as someone stated, a dealership might very well use it as grounds for not covering a warranty or charging you out-of-pocket fees for creating additional, unnecessary work for them.

Formula271

I have to second the comment of the spray foam being a terrible terrible idea.

Aside from there being much better materials for both vibration reduction and sound improvement and the aforementioned mess / potential dealer warranty issues should you ever need to deal with service department, the health concerns of being inside a small interior space with outgassing spray foam product should cause pause.

Spray foams are made with diisocyanates, which are a leading cause of workplace asthma and are toxic to humans. You might not even be sensitive to the chemical at first, but continued exposure actually increases sensitivity.

Consider too that the interior volume of air in a typical house (where u might more appropriately use spray foam) may easily be several hundred times greater than that of your NX....and that your NX rear hatch in the hot sun will reach easily 120F+...that u share that hot interior air with the "great stuff" foam...

Not to mention...how about the effect of continued exposure of the other oil-based products in your interior (almost everything) to the chemical outgassing?

You've basically ruined your car.

corradoMR2

Good points above including from Pinhead and computerwi. This DIY has some risks, use your own judgment for sure as it is not for everyone.

It's a good point to the highlight the toxins. When this foam is applied in large applications in a home, for example an attic or basement wall, the family must stay away for 24 hrs or until it's cured since it is during this time toxins are released. For this particular DIY, one can validate if the foam is cured with a shish kabob stick. If dry after inserting, it's cured.

Yes, denim or fiberglass insulation are great for the reason you state since it's removable but it depends the application. I've applied it to several of my vehicles including my past RX and the NX recently to the B-pillar (see below pic but that's for another DIY) . I've also applied the Great Stuff foam in the past with success eliminating the infamous 3RX B-pillar ticking noise with this material since the tick was due to a missed spot-weld in the pillar (denim nor fiberglass resolved this specific issue as they were "loose").

But be careful in recommending the denim/fiberglass in relation to the rear hatch door without stating its own risks or being specific on how and where it will be applied. For instance, even taped or with adhesive, it can eventually move and interfere with the door locking mechanism unless you've found a way to securely shield the mechanism around top, left, and right sides (like below pic of my NX B-pillar with the cork underlayment shielding the top of the seatbelt mechanism). Please post here or create a separate DIY so we can all benefit on alternatives!

NickTee

Great Stuff can also break free and cause issues due to the very reasons I stated regarding the drying. It's much less likely for denim insulation sheets applied with a quality spray-on adhesive, which would require removing the panel, to break free and move.

Formula271

I really hate to be the rain on this particular DIY parade, but this picture is very alarming. It's looks like this is the Fr retractor in the b-pillar lower area.

A few things come to mind....

1) This retractor has a pretensioner....basically a pyrotechnic device designed to fire in the event of a collision in order to take out the slack in the belt system prior to the belt loading from impact. This pretensioner creates A LOT of heat when it fires. There is a reason there is clearance around the retractor, and pretensioner, in particular. In this picture, the material stuffed around the retractor may catch fire quite easily. It would be horrible if you were not conscious, or otherwise unable to exit your vehicle after a crash and then this area started burning.

2) Is that more "great stuff" foam in the pic, too? If so, these are just a couple of the conditions this (or any semi-rigid "plastic" like filler) may create in this area...
a) There is clearance around the retractor so it can function properly in a crash (not just the fire concern reasons above). For example, in a side-crash, the 60mm of crush space that previously existed in the b-pillar structure will allow the retractor housing to remain intact. If that same space is now filled with "great stuff", as the side-member intrudes during a side-crash, the block of "great stuff" will travel with it, potentially crushing the retractor housing before it has had a chance to restrain the occupant.
b) That same block of "great stuff" now couples the inner and outer b-pillar structure in a way not intended. So, instead of the outer b-pillar crushing as intended, energy is transferred to the inner immediately. Now, both parts of the structure move together (or at least more together). This increases the speed of intrusion of, for example, the Fr Door Trim. So, the door trim has now intruded more than it otherwise would have at any given time. Your front seat side airbag now gets trapped because, in the 4ms it takes to get out of the seat and cover your pelvis and torso, the door trim is already in the space the airbag needed to deploy.

So catching fire, retractor crush, side airbag trapping....these are just a few of many potential side-effects.

There are many many helpful DIY's, and I really don't mean to be a nudge. I'm being genuinely sincere when I say please don't do this.