Annoying hum with air handler-better when filter removed

Video with audio in link. This is only a Merv 7 filter but the hum/whine gets better when the filter is removed. HVAC guy says it is lack of return air. He suggests tapping in to the return main right below the flex coupling and creating a return through the adjacent wall(which is a bedroom/office). Note that this system in the zone 2 which services the upstairs and we can't get a new return on his floor without major cutting through drywall(and the way the joist run it would be a nightmare). The bedroom/office on this floor with the proposed new return is served by zone 1 HVAC with the air handler in the basement. This bedroom/office is a decent size and has 3 supply vents and 1 return(for zone 1). Both zones are heat pump systems. Do you think this new return will solve the whining noise? I know it's not ideal but our main concern is to stop that horrid noise and not rip our house apart to do it. Excuse the gross-ness, this is a large utility room in a house being renovated.

https://imgur.com/a/air-handler-heat-pump-noise-5Ld50Ya