1. There is a tiny whining sound coming from furnace when furnace is running, is it normal?
No, it is not normal. The whining sound is coming from the blower motor, which can be caused by:
The blower wheel is grinding the housing.
Blower motor may be worn out.
Capacitor not good.
2. When I turn on cooling, outdoor unit runs but indoor unit makes high whining sound but no air coming out of the vent
Indoor unit blower motor and blower wheel need be replaced.
3. There is a hissing sound coming from my outdoor heat pump unit, should I call the repairman?
First, check if the temperature inside the house is cool with the AC running? If the temperature is cool, then check if the outdoor AC unit is making a hissing noise? If yes, then cut off the power and remove the material found (leaves, paper, etc.) then turn the power back on. If there is nothing inside the AC that is making the hissing sound, then there is nothing wrong with the AC unit. If the AC is not cooling, then call the repair technician.
4. Strange Sound Coming From A Pipe that connects to The Air Handler when air handler runs
You need to clarify if this is a PVC pipe or copper pipe. If this is a copper pipe, and the noise is coming from the refrigeration, you can add a little refrigerant to reduce the noise. If it is a PVC pipe, then you can add U trap to stop the noise.
5. There is rattling sound from the duct/pipe
First, identify where the sound is coming from. If the sound is coming from the duct, remove the register that is closest to the rattling sound and check to see if there is any material inside the duct making the rattling sound. You can use the vacuum cleaner to remove the material. If the noise is from inside the air handler/furnace, then open the unit cover and find out what is causing the rattling sound.
6. My compressor is making an incredibly loud screeching noise. Is it dangerous and why?
Your compressor may have:
System has refrigerant overcharge
No refrigerant at all.
7. There is a “thud” sound after the furnace completes each heating cycle, around 20-30 seconds after the blower has shut off. This is a new sound that started happening around 2-3 weeks ago.
This means that the return duct needs to be reinforced. When the unit stops working, negative pressure in the return duct may cause noise when the negative pressure returns to the duct.