Trane air handler too noisy

I have a 2000 sq foot ranch house in Phoenix, built in the early 70s. Until a few weeks ago the house used the original Carrier split system for cooling. I believe it was a 4 ton unit. The duct work in the house is the large bent metal type, large enough for a small child to crawl through. The air handler blows up from a closet in the hall to a "T" of duct work that goes down two hall with ceiling registers in each room. The old system was quite--as is our large Master Cool Evap cooler that also feeds into the duct work. The new Trane air handler has a large amount of air noise coming from the registers. There is little noise at the intake. The new system measures between 69 and 72 dB noise at the registers, the Evap cooler noise level is below 60 db.
The squirrel cage blower from the old Carrier system was about 13" across and was belt drive, the new Trane blower is about 9" across. It looks like the old low velocity/high flow blower was replaced with a high velocity/high flow blower and this is causing all the noise. Does anyone have any ideas on how to quite down this system? The big open ducts transmit the noise very well. I've been told by a number of AC companies that no one makes a low velocity high flow blower anymore. The blowers are all designed for the flexable duct work that most homes are now built with. So far we've tried insulating the inside of the duct work where the air handler connects but this had little effect.
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In large commercial applications, sometimes a sound trap is installed inline in the duct system. Such a critter may be available for your tin duct system.....
http://www.healthsystem.virginia.edu/internet/hep/specs/current_specs_2004/15072-043003.pdf
is but one of many sources of info......
http://www.wbdg.org/ccb/DOD/UFGS/UFGS%2023%2031%2011.12%2040.pdf
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Thanks, I'll follow up on the links.
snipped-for-privacy@gonefishin.net wrote:

http://www.healthsystem.virginia.edu/internet/hep/specs/current_specs_2004/15072-043003.pdf
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