My recently bought 07 Silverado 1500 classic 4x4 makes an annoying whistling/whining noise only when its shifting. Everytime it shifts to a different gear. Fluid level is good, and no other problems. Transmission seems to be fine, No codes. Just the noise of shifting, sorry thats the best way I can describe the high pitch it makes while shifting. What is causing this , And is it a serious problem ?
Thank you