The cheapest PROPER way to reduce cabin noise seems to be Second Skin Damplifier, Luxury Liner etc. Same quality, but significantly cheaper than Dynamat.

Then there are ways using butyl-based home insulation, complete with carcinogenic vapors.

 

Not easier, but there are Lizard Skin or Second Skin's Spectrum coatings.

 

If you are suffering from a mechanical whine - fix it!

Modern hypoid gear oil in the differential can work wonders (if it hasn't been left for too long)

New oil in the gearbox / transmission won't hurt either.

Propshaft bearings can squeal as can wheel bearings - replace / re-grease

As for other noise - the most likely problem you'll be experiencing is air borne noise. The W123 is quite refined for its time - but after 25+ years of life any car will start to get a bit "leaky" => clean your door seals with Aerospace 101 (or an equivalent product). Replace damaged / broken seals.

(That's two cheap options for you)

 

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Even so, there's a lot of tyre/road noise, enough to dominate the mechanical noise.

I think installing heat/sound insulation under the engine bay would be a PITA. All those hoses, wires and cables...

I'm certainly looking into Luxury Liner Pro for my 200's doors. I'd hate to add too much mass, but even a slight reduction in ambient noise penetration would be wonderful.

 

I still think an air borne noise route is more likely. An easy and quite quick check for this is to tape up the door gaps and see if it makes a difference. (Please note this is unlikely to make much of an effect on tonal - whining screaming - noises they are better tackled at source if you can)

 

Michelin tires

 

if you are under budget, like me, you can try to get some duct insulation from home improvement stores for the road and body noise. They are similar to those Dynamat thing, but a lot cheaper. I put them on the floors, firewall, hood, under the rear seats, and the spare tyre compartment.

For door seals, if they are cracked, you can try to use some weather stripping to cover the door too, that really works if you have cracked door seals. Once again, this is really a cheap, low budget improvement, I believe the real solution is to replace the old door seals. Also try to get some foam based weather stripping from Daiso, place it in between the inner door frame and the body, that might also help...

Finally, some how the lower part of my under dash panel was missing, I made one out of card board, covered it with some duct insulation and foam, and it works! With no cost at all it acts like a second...ish wall between the engine and your ears.

That's all the easiest, cheapest way for me to reduce my cabin noise, hope it helps! : D

 

if you are under budget, like me, you can try to get some duct insulation from home improvement stores for the road and body noise. They are similar to those Dynamat thing, but a lot cheaper. I put them on the floors, firewall, hood, under the rear seats, and the spare tyre compartment.

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Just a warning - a heads up if you like

Generally this type of stuff is a bitumen based product. This isn't a problem until there's a fire. I think you'll find that the automotive version has to be a little bit more fire retardant for this reason. Now I know you're not planning to have an automotive fire but...

 

Adding a picture of what I've done to the boot. Hope it helps!

 

My buddy did the home depot insulation all over in his 300CD including the doors. I notice a difference in my car just by throwing in 2 more sets of floor mats (palomino oem mats, and oem rubber foul weather mats)...

 

Well, i currently run the regular OEM mats and rubber mats on top.

Have fresh ATF in the trans and gear oil in the diff. If i was to install dynamat/second skin, will it work if i just glue some to the engine bay firewall?? Or, is it an absolute must to strip the entire interior to install the stuff.

As for wind/road noise, i was goin 80mph today and let off the throttle. It's a HUGE reduction in noise if the motor is just idling while going highway speed. So... i'm not a huge believer in new door seals yet, especially as the current ones aren't ripped.

 

As for wind/road noise, i was goin 80mph today and let off the throttle. It's a HUGE reduction in noise if the motor is just idling while going highway speed.

I'm pretty sure that's because there is no combustion. The governor in the IP stops all fuel flow to the injectors at such a high RPM and little power demand, so the engine is coasting, pumping air, with no sounds of combustion. My newly rebuilt injectors noticeably reduced and softened engine noise on the highway.

 

Just install a louder stereo.

 

Fixed my door seals, that was the most significant noise reduced I performed to the car since ownership.

The transmission tunnel pretty much is under-insulated - add some when the carpet is out as well as the firewall inside the dash - that should quiet the drivetrain noise.

 

Wait, that's gonna be a buttload of work to strip the carpet and stuff out to put insulation underneath. Will it help if i just put some of this dynamat or Secondskin on the underbody/exterior portion of the transmission tunnel???

 

I think jacking up a car and put on some insulation on the underbody is also a buttload of work, too...don't you think removing the carpet is a lot easier? Most of them are removable... like many other cars