Loud noise We have a new home with a Nordyne split system heat pump Model FT4BD-030K 13 seer When the unit goes on it makes a loud noise for about 5 to 10 seconds. Is there a fix to this problem?

adding a tvx will not help. the sound you here is the pressure equalizing and that has got to happen for the compressor to start again the next time. A tvx will give you a higher efficiency because it can adjust to changing temperature conditions. Only way i know to quiet the noise is to try to insulate the lines better.

need make and model numbers on both units.

This must be a heat pump? Sometimes the unit can be more efficient with this combonation. What you are probably hearing is the reverse direction of the
refrigerant going back through the liquid line.

If in cooling sometimes you can hear a gurgling sound going through the expansion valve, sometimes
this is a sign of low refrigerant or the system is fine..

If you recently had the outdoor unit replaced and noise is an issue, check to see if the unit has isolation pads installed underneath the unit whether
it be on concrete slab or on brackets mounted to
house. Sometimes the new units come with compressor that has a jacket installed over it

Depending on make and model sounds like a check valve clicking. It can sound like it is coming from that area. You say your unit is 16 years old. Honeywell did servey on unit 10 years and older and found out they loose 25% effeicency after 10 years. You may think about changing it out. With the new tax credits you can get a 16 seer unit for the price of a 13 seer. I went from a 10 to 15 seer and my power bill dropped 40%. Rus.

I install them every day and I have not had one make a loud grumbling sound. Sounds like you might have a low voltage (Thermostat) wiring problem. The only thing different inside the indoors unit from heat and cool is the fan speed, electric heat when on. The fan might be loose or out of balance and it only shows up at low speeds. Either way, the noise is not normal.

I sell Rudd equipment. You have air in the system or faulty TXV. Replace TXV and evauate system. No more problem. Rusty

Your problem is the TXV. I just had person with the same problem. Replace TXV no problem Rusty

i dont think so that variable speed air handler is a nightmare when(not if) that motor goes bad its 700.00 to 900.00 the regular 3 speed one your getting 125.00 and it will last 10 to 15 years ....... if you realy want fun install a 17 seer system ,you will have your repair guy on speed dial

Well you may want to have a tech come out and check the freon level, but mostly when going into defrost, some units make alot of noise, the freon is reversed in the unit by way of the reversing valve, it makes a whooshing sound like freon is draining off, as far as the knocking noise, could be as I said in the beginning, might be low on freon, but it could be that, this particular unit does this, I have had units make some really strange noises in the past but functioned perfectly, hope this helped, please let us know, thanks again,
mr.grzz