Whirring noise!

I have a 2001 Z71, 5.3 with 107,000 miles on it. For the past 6 months I can hear a high pitched whirring noise from in the cabin when Im driving. The pitch stays consistent with the engine rpm. It sound like its coming from the rear of the engine or the front of the transmission. I cannot hear it when the hood is open. I thought it might be the alternator so I changed it but the noise is still there. The truck still runs fine the noise is really annoying and Im worried it may lead to something major. Thanks.

maybe the fan? these clutch fans get noisy sometimes

I know this might sound weird, but check your windshield wipers... the slightest amount of airflow change will give you a constant whirring sound when your driving. Have a passenger reach out and lift the wiper up while your driving and see if the sound goes away. Do the same on the drivers side (carefully!).

maybe the fan? these clutch fans get noisy sometimes What was the noise from????

What was the noise from????I have a 2002 silverado making a simmilar noise. It is like a howling whirrling noise like wheel bearing or trans???

I know exactly what you are describing. I have an '02 2500HD with the Allison and the 8.1L that has had the "whirring" noise since I purchased it last May. It is definitely coming from the bell housing area and has grown louder recently. Not sure if matters that it is an Allison vs. GM trans. I changed the fluid and the old fluid and external filter was in great shape and the change had zero effect on the noise. Trans shifts great except for a weird delay when shifting into reverse. Almost like it shifts into reverse twice?? Anyway, took it to the dealer and they have no idea but are yanking it out this week. My thoughts lean towards the torque converter, but who knows. I'll keep you posted. Oh and thank god for extended warranties!!