My mortgage is with Chase and they sent me an offer to lower my fixed rate from my current 5.6 rate down to 4.8. There are no closing costs and other than the rate change the terms are exactly the same, other than of course I am starting my 30 year loan from the beginning again. I am 4 years into my current loan so if I continue to make the same payment I will pay it off approximately 3.5 years sooner and save about 50k. Is this a no brainer or is there a catch I'm missing. According to Chase it is because I make my payments on time and they don't want me to go somewhere else since rates are going down. Any expert advice?

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1984 300TD 1981 240D