That’s the million-dollar question for every homeowner! I went through this exact mess last year. That whistling usually means your bearings are shot or there’s an air leak, which basically kills your efficiency. A huge lesson I learned is that the performance of a new furnace depends way more on the setup than the brand itself.

I actually spent a lot of time reading through the expert advice on this page https://roadfood.com/author/furnace-installation-service/  it goes into great detail about why professional installation is so critical. It turns out even the most expensive furnace will run like garbage if it’s not properly calibrated to your home’s ductwork or if the sizing is slightly off. After looking through that info, I realized that investing in a proper installation was better than paying the "gas tax" every month with my leaking old unit. I ended up replacing mine, and it’s so quiet I barely know it’s on. Plus, the drop in my monthly bills was very real, not just marketing fluff.

Thanks a ton for the link! It sounds like I need to stop procrastinating and start looking at a replacement. I’ll definitely check out those details on proper mounting before I hire anyone.