My 01 Tahoe 5.3 has been making a noise almost exactly like the nice hum when I added the KN Air Intake sys 10 yrs ago. It is just getting louder. It is also making a "GURGGLING" noise (loss of a better word / description) when I let off gas pedal at times. I dont know if it is an ignition sound or what but truck is definitely lost some pwer still cruises down the highway at 80 aprox 2,400 rpm but loss of excelleration power and when you accelerate that is when the humming noise gets loudest as you gas it. Anyone have any info, no check engine light or anything like this...I am stumped (I cleaned air filter, MAFS, TB and installed new PVC valve).