my a/c unit has always made a lot of air turbulence noise both at the central unit site and at the indivual vents into each room. Operationally the a/c cools very good and heats very good, however the a/c fan sounds like it is churning air volumes greater than the coils/heating chamber's capacity to accept, pass or handle. The coils are serviced every spring. The vents in the rooms emit a strong hissing sound as if air volume is too much. I explained all this to the serviceman in the beginning but he says the unit is working like it should and I should accept the noise.
the open area under the a/c unit is approximately 4' wide, 5' deep and about 12" in height sucking return air thru a 16" x 36" wall intake vent. there is another 16" x 28" vent that i have recently closed off. the cooling efficiency is better without it and runs less with no iceing on the condenser coils. when the unit is in the heating phase with the gas intake valve wide open the heated air gets too hot and the thermostat shuts unit off before the entire house feels warm. i solved this by daily slowly cutting back the gas volume, which serviceman did not approve, until a comfortable house temperature is achieved and maintained.
i plan to instal a wind tunnel 36" wide at intake vent opening and reducing tunnel down to the same width as the opening into the bottom of the a/c. due to the expence and tight working area etc to install this tunnel I would like to hear some opinions on my situation as to wheather this will help eliminte the air turbalencely noises as well as the eco sound. I would appreciate any suggestions.

Again tell us why you closed off the 16" x 28" return? Andwhat did you gain by closing it off
It is sounding to me like you either have to small of duct work (supply) or you don`t have enough return

Maybe your fan speed is set up to high. Not sure why your closing off ductwork. And condenser coils freeze in heating mode on a heat pump. You have gas. Do you mean evaporator coil?

o.k. I will give you more history of my problem. I bought this house in 1986 and it had a 3 ton American Standard heat and air unit. This unit made even more noise than the current unit. In 2004 a new 3-1/2 ton Rheem SEER 13 with 4-1/2 evap. Coil replaced the old unit. This unit is was almost as noisy as the old unit. There is a wind turbolence noise eminating from the fan area. There were two 16"x28" return air ducts and I temporairly plugged one of them. This did reduce the noise level but not to an acceptable level. I enlarged the remaining vent to 16" x 36" for fear of evap. Coils iceing over. It sounds to me like the fan is trying pass through more air than the evap. Coil/heating chamber area can handle. Additionally the room vents seem to be holding a back pressure resulting in the undesirable hiss at each vent. The unit is cooling perfectly today but it should not be making this noise. In the winter if I run the furnace with the gas inlet valve wide open as service man instructed the gas burner makes too much noise and the heated air is too hot at head level and the floor level is cold. I can slowly close off the inlet valve until the lower temperature heated air will warm the whole rooms(s) before the thermo shut the unit off. I do not know if the fan motor speed can be changed. I am a the point that I think the cheapest route to fix the problem is add additional new duct work to extend air conditioning to a 500 s/f enclosed sun porch with a return duct that will return air from the porch through the elevated floor and into the intake area below the a/c..

Wait.. so you went from a 3 ton to a 3 1/2 ton with a 4 1/2 ton furnace? That makes no sense at all. If that is the case no wonder you have issues. Before you go making all sorts of changes I suggest calling another company out and having them go over entire system and suggest what is wrong. Either something needs to change with ductwork or system. Either way needs a real tech to look at it and make suggestions on where to go from there.

The a/c unit is a 3-1/2 ton with a 4-1/2 evap. Coil. The heating unit is a 80000 BTU gas burning furnace.

I understand that. But you originally had a three ton unit inside and out? Your ductwork was designed for that unit. Any altercation in size of unit could need a change in ductwork. And why a difference in a ton between inside unit and evap coil?

I seriously recommend you get someone out other than the company you use to look at system.

o.k. I agree, however, I am going to install the intake wind tunnel as this will not be very expensive and may eleminate the echo sound from the open area under the a/c unit. Thanks for everyone's suggestions.