问:- 1991 GMC K2500刺耳的桑巴引擎

我更换了一个刺耳的皮带在几周前我的卡车。这是一个老,疲惫不堪。但然后我的卡车开始一个新的不同于带刺耳的尖叫声。我脱下皮带,旋转和张紧装置滑轮研磨,所以我替换。但它并没有帮助。我把皮带,再次旋转滑轮。交流发电机是刺耳的,所以我买了一个新的。和引擎仍然是刺耳的噪音。我将在一个新的水泵几周前,但不能制造噪音。这个刺耳的唧唧声刺耳的噪音,它会有所不同取决于rpm。 It goes away sometimes when accelerating the car. I had bought a cheap belt, so I better pick up a better brand. That might possibly help. The belt tension is good and so are the water pump, idler pulley and the alternator that is refurbished. My truck has 271500 miles on it and it’s a 5.7 TBI. Do you have any ideas about what might be making the screeching or rather chirp noise?