Around August of 2007 my central A/C broke. A service company came to the house and installed a 15 Seer Rheem split A/C system, a high efficiency unit that helped me reduce the electric bill by 35%. I was happy with the new unit until I noticed a high pitch noise coming from the furnace; asked the vendor about it and said that was normal. Tried getting used to it for another 2 months until it suddenly stopped.
Rheem A/C air handler and its annoying high pitch noise
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