Does the company work with existing windows, e.g. to replace sashes or upgrade the glass? Or, is it only whole window replacement? I have a 2-year-old house with would simply like to improve the noise buffering.

To answer your question it's best to call for a replacement estimate. They have excellent choices for sound and cosmetic. They replaced mine about 4 months ago and I live on a busy street. Couldn't be happier. This company does not scam people I had other estimates with other companies and they were way over priced. Good luck.

Its only a whole window replacement. But they do it all custom made

I would look elsewhere.... UWD are scammers