I just bought a new house and My A/C unit which is a Goodman unit is making a spitting noise while it is running. I had my Heating and A/C company look at it and they said there is nothing that they can do about it and that it is normal. They said that the noise is made by the freon spitting through piston coming from the A/C unit into the main furnace whole house fan. They said that the noise will be made every time the unit kicks on for a few minutes and then it will make the noise intermentelly until it kicks off. When the next time it cycles on it will make the spitting noises all over again. The noise is not bothersome as it is coming from the unfinished basement and we can not hear it from the first floor. Although, we are going to be finishing the basement soon and I am concerned that the noise will become quite pestering when we are down there more often when it is finished. Has anybody had any experience with this problem and is there any way to fix it? Should I demand better service from the Heating and A/C company that is servicing my system? Thanks

A hard shut off expansion valve might take care of this problem by keeping the refrigerant from migrating, this would keep liquid at the valve on startup. If you have a piston metering device it is not to difficult to do .
This may not solve the problem because the refrigerant is changing state at this point and it depends on the construction of the coil. Ask your contractor what he thinks. When a hard shut off txv is installed it is necessery to install a start capacitor on the compressor as well since it would be starting against a head pressure.
This type noise is more apparent when the system is under charged as well.

I've never heard a unit make this much noise that could be that loud and annoying. Usually the pistons that meter the refrigerant don't slam open and closed. Has anyone checked the superheat? Is it properly charged? Before installing the TXV you need to consider several factors, is the unit just a air conditioner or is it a heat pump that heats in the winter as well? Depending on your location and operating conditions you may also need a liquid receiver and /or a suction line accumulator. By installing just the TXV you could cause liquid refrigerant to slug back to the compressor which can damage it. You also don't want to void any warranties that may still be left on the system

Thermostatic expansion valves are offered as an upgrade accessary to obtain the higher SEER numbers, they are listed as a necessity in the ARI book to reach these numbers on some evaporator coils. By adding the manufacturers listed TXV it does not effect warranty.
The addition of a receiver is totally unnecessary, the accumulator is factory installed on some condensing units. The addition of a TXV does not cause liquid slugging to the compressor.
Melenfert mentioned he has a furnace (not heat pump)

I guess you don't understand how a TXV works and what superheat is and what happens to a system when the ambient temperature changes. Your correct ARI list the TXV as a necessity on SOME evaporators. Most of these system the condenser is sized to handle the extra refrigerant that may be in the system, using the TXV in a cooler ambient temperature without the receiver can cause slugging do to overcharging.

Contractors working with the new high efficiency air conditioning systems today are aware that the use of TXV's are necessary in all high efficiency air conditioning systems above 14 SEER and higher to get the maximum efficiency . How many residential A/C systems have you seen with a receiver ? (NONE)
The pressures in systems with piston type metering devices fluctuate considerably due to the ambient where as systems with a TXV are much more stable , When the suction pressures can be maintained in the 60's on a hot day using a TXV as compared to a piston metered system in the 70's due to the higher head pressures, the Txv system will be cooling better and more efficiently (pressure -temperature relationship)
A TXV system is charged by the sub cooling method and not by the super heat method, when some one overcharges any type system it is detrimental to the compressor and to suggest that it is necessary to overcharge a TXV system is not informed and should be trained in the proper way to charge a system .

I need to clarify what my system is. I have a heat pump and a gas fired furnace. My heat pump which is serving as my airconditioner currently has a 13 SEER rating. It is made by Goodman (model # GSH130481AC)

When we first moved into the house a straight air conditioner (not a heat pump) was hooked up and it made this same spitting noise. Shortly after we moved in the Heating and AC company removed the A/C unit and installed the heat pump unit to make it a dual fuel system. This was done because this is what the house was listed as having when it was advertised for sale. Once the heat pump unit was installed it made this noise and the Technician told me it was because freon was low. He charged it up and the noise died down. A week later the noise came back and now it is doing it every time the system is in cooling mode. I had the technician come back because I thought for sure there was a leak and made the freon low. He stated the freon charge was good and that there was nothing he could do about the noise because it was being caused by the freon going through the piston

Since you do have a heat pump and the system seems to be cooling properly and your service person said that it is fully charged then there is not much you can do , you could ask him if the pressures were slightly lower then normal which might indicate a low charge or some restriction in the orific. It is not hard to pump the system down and inspect the orifice, if it is the design of the coil, then you could replace the coil as a last ditch option.