[chas]

Thanks Anthony - great thoughts. Fortunately there is another utility room on the other side of the HVAC unit and it does have a fresh air intake line.

The door suggestion is a good one. I'm not looking for total all-out sound isolation...just a reasonable quiet room. But I do plan to use acoustic caulk on all gaps, openings and under the drywall.

I'll have to look into salvage yards around here - thanks again for the input.