Fixing Wall Shudder

If it’s a newer build and the walls are internal, then they can be very cheaply constructed. If they’re non-load bearing, then the studs may be 24” on center, rather than 16”. In addition to that, many times internal walls are not insulated. So you could be dealing with multiple non-insulated walls with studs 24” on center and possibly only 3/8” drywall. The combination of all that can provide you with a really crappy room.

I’d investigate the wall stud spacing and see if the walls are insulated, first. If they’re not insulated, you can have insulation added to them. Or, you could choose to remove all the drywall, add studs, insulation but also acoustic rubber before the drywall goes back up. That stuff comes in rolls and is just nailed up to the studs before the drywall is installed.

@paradisecom 

If they’re non-load bearing, then the studs may be 24” on center, rather than 16”.

That is my quess. Code allows for non-bearing walls to be constructed with studs @24” o.c. As a residential designer, also involved in building, personally, I always call out interior walls to be @16” non-bearing or bearing. Just better quality construction IMO, but it is permissible by code.

Since you don't want to tear down walls, (and I can sympathize), your easiest solution is to add an additional layer of sheetrock, and perhaps sandwich a sound dampening layer.

Bob

I agree with a second drywall layer.

Use construction adhesive generously between the 2 layers along with 2 1/2" drywall screws.

That should firm up things nicely along with less difficulty.

   LP

I ran across a heavy material sold just for this purpose, on an audio website.  I can't recollect what's it's called but I remember it wasn't cheap. Comes in a big roll, you cut and install. Not sure if it's glued or fastened. Like a thick dynamat.

Um, yes this is fixable, but the description I'm reading is kind of bullshit.

Stick with and fix the basics.  Bass traps, measurements and DSP along with proper speaker/subwoofer/room integration.

True wall flex/rattling issues sound like rattling.  A person holding a part of the wall can easily fix it and the normal fix is better drywall screws.

I'm with Erik, unconvinced this is your problem without more information. How loud are you playing your music? Btw, most of the suggestions above aren't great. Tell me a little about your place. I've been in residential construction, self-employed, since 1989.

Use a frequency generator app on your phone connected to your audio system and run through the frequencies noting the Hz and location of the resonances. This will help you identify the failure points.

@mkgus Second generation building contractor and music enthusiast here. This would be a simple clean fix. Use that blown in insulation in the stud bays , you can either rent the machine or have a contractor do it , then do a quick mud and tape job on the holes that were drilled for the insulation and then go over the whole wall with new 5/8 drywall like one if the other posters suggested, it’ll work great. Sometimes the guys like to leave empty beer cans in the stud bays , this’ll keep em from rattlin around at high volume ( kidding 😀).

The good news is that non-load bearing walls are easy to replace.

 I had a related noise issue with an exterior wall. My fix was to put on another layer of sheetrock vertically on top of the existing one. I used a green substance used just for this application. I forget the name of it. it helped a lot with the absorption of unwanted noise. Using a different thickness of sheet rock, like 5/8" instead of the usual 1/2" will help also. But the proof was in the difference in noise transmission. The reduction in noise was immediate. 

 Also included was the blow in insulation mentioned in another comment. To cover the lower holes made by the installer (half of the holes are near the ceiling and half are about 3' above the floor), I made a heavy duty chair around the room, and caulked the chair railing top and bottom. I made a wider than usual Crown Moulding for the top half. It has worked out great for the rooms involved.

This is why I have my systems in the basement. Concrete floors and walls sound best.

+1 @noromance 

Maybe they didn't use construction adhesive to bond the drywall to the studs.

To recap:

Your description is of known and common room problems, therefore fix those first before you go looking for exotic and previously unknown issues.

Spray foam

Thank you. A lot of good information here and I will take everything into consideration. Concerning the idea of adding a layer of dry wall, one concern I have is that if I later decide to tear down to the studs, the extra layer will be for naught. Would 24” O.C. be a deal breaker and require opening the walls and adding more studs/cross-bracing? What should be done before adding an extra layer of drywall?

 You never know what you will find 'behind the curtain' in craftmanship. When I bought my old house, it had numerous repairs done by someone who didn't give a care. I would use the side of my fist and thump along the wall to listen for trouble. You will hear it if it's there. The trouble spot was actually in a small clothes closet where the previous owner used 1/8" Masonite instead of sheetrock! Sounded like a drum. A little upset, I took that out and replaced it with concrete wall board. What? you don't think that this would not react to music with bass? 

 Point here being that you really don't know what is going on in some situations until you have investigated it yourself. Same with electrical, plumbing and more. Just because there was a home inspection doesn't mean that you get the full story.