SM465 whistling at highway speeds


New member
Sep 22, 2013
Hello, I have a 84 C10 Long box, 305, with a SM465 transmission. At freeway speeds (60+) in 4th gear after cruising for 5 minutes or so, there is a noise I can only describe as a tea kettle whistle, or high pitch, high frequency rattle. It gets louder as accelerator is depressed. Noise seemingly coming through shifter, at speeds 0-55, noise is not present. It’s been doing this since I got it in high school in 2007, and I’ve never had any other transmission problems. Over New Years 2021 I drove it almost 300 miles straight without stopping down i5 at ~75mph, whistling the whole way. Any idea what is wrong? I can afford a full rebuild if it needs one, but if someone has experience with this type of noise to send the transmission or repair shop in the right direction it would be appreciated