I can provide some general guidance on this matter.
The weight capacity of a 2x4 framing with wooden studs 16 inches apart and a 9 ft ceiling can vary depending on factors such as the quality of the lumber, the grade of the wood, and the overall construction of the structure. The weight-bearing capacity of the framing will also depend on whether it is load-bearing (supporting the weight of the roof and upper floors) or non-load-bearing (supporting only its own weight and interior walls).
QuietRock 545 panels are a type of soundproof drywall that is denser and heavier than regular drywall. Before installing these panels, it's crucial to determine if your existing framing can handle the additional weight. If you're unsure about the structural capacity, it's best to consult a structural engineer or a licensed contractor who can assess your specific situation and provide appropriate recommendations.
If your current framing is not capable of supporting the added weight, there are potential solutions. You could reinforce the framing with additional studs or cross bracing, or you might need to use lighter soundproofing materials that won't overload the existing structure.
When it comes to soundproofing projects or any modifications to the structure of your home, safety should be a top priority. Always seek professional advice to ensure that any modifications or additions are done safely and in compliance with building codes and regulations.