Had a YORK 14 SEER system installed 2 months and from day one the compressor makes a noise like someone hitting a empty 55 gallon drum when unit shuts off and comes through ducts. The installer says it is normal? :confused: Because of back pressure. My 9 year old 11 SEER Rheem was quite as a mouse. Any ideas?

Noise that loud is in no way normal. It only does it when it shuts down right? WHat is the model number of this unit?