I live in central Florida in a typical ranch style single story block home. The home was built in 1974 and was originally 1690 sq ft. We have upgraded the windows, insulation, etc and just finished adding approximately 530 sq ft to bring it to approx. 2220 total air conditioned space. The old a/c unit was a 3 or 3/12 tons installed in 1989 (it finally died a few months ago). The new unit is a 4-ton 14 SEER Ruud.
The issue is the return vent which in the ceiling at the beginning of the hallway. The filter measures 20x25 and this is the only return in the house. The old unit could not be heard when it cycled on/off. The new one almost wants to suck the filter inside out. The hallway is not long, perhaps 18 - 20ft and all 3 bedroom doors are towards the end (one on each side and one at the end). When the unit cycles on it creates a vacuum noise and will actually shut my bedroom door if left a few inches open. While laying in bed at night it make a slight roaring/vacuum noise. It almost sounds like a small jet engine. You probably get the picture by now.

I asked the person who installed the new unit what I should do. (the unit was installed on the side by the a/c guy from my work) He advised that the only way to rid the noise is to either put in a larger return or add a second one.

I have debated on each and tried to research how to's but keep coming up short. If I replace the original return then I will have to limited to the width of the rafters and then by the width of the hallway. I only have a few inches at best on either side of the return grill to the hall walls. I will also have to disconnect whatever tubing/box is attached to the return grill and build a bigger one and then reattach everything. (sorry but I am not to familiar with a/c terms). If I decide to add a second return, obviously in another room, am I limited to where it can be? I read not to place them in bathrooms or kitchen but what about the ceiling of the laundry room? How large/small of a return will I need? I read on a few forums that minimum standards are 144 sq inches per ton. That comes to 576 sq inches for my 4 ton until and my current return is only 500 sq inches. Would a second return of 12x12 or 15x15 be sufficient? Would it depend on how long the run is from the second to joining the original? Do I have to run square box tubing to join them or can I use a certain size flex hose? I did spend several hours trying to research before I decided to post. Any help would be greatly appreciated.