My 1999 Blazer 4WD V6 starts fine, runs great and is quiet as a bug while it is warming up. Once the engine reaches normal operating temp (200-210), a strange noise (I thought it was a bad belt idler arm pulley) appears...the noise gets louder as I load the engine. I have also noticed clicking and catching of the accelerator (as if the cable is catching on something...again, only after reaching temp). The best way to describe the noise is similar to a dried-out speedo cable noise...or a bad bearing noise. It is coming from the engine compartment and ONLY after engine reaches temperature...I can almost predict to the minute when the noise and catching of the accelerator will appear based on my temperature gauge reaching temp. Any ideas or similar experiences??

 

The noise described above still persists...again, all is well from startup to normal operating temp...once at temperature, any loading of the engine (acceleration from a stop...passing from normal cruising speed) causes an intermittent 'rattling' or 'clicking' noise from the engine compartment. I have removed exhaust heat shields...tightened every bolt I can get my hands on (including motor mounts and exhaust manifold/collector flange bolts, starter)...replaced the belt tensioner, distributor, timing chain/gears, removed valve covers and inspected lifters for looseness/abnormal play...verified the oil dipstick tube is clear of the exhaust manifold (I really thought that was the cause when I found that one!)...when the noise appears, I have found that rough/worn driving surfaces are matched by the intensity of the noise (i.e. when on a rough patch on the freeway, the noise fades/intensifies to match the roughness of the road). Whether in 2-Hi or Auto 4 Wheel drive or 4-Hi, the noise exists. I want to say that the noise appeared after installing the 2" body lift, but nothing is bound, resting on the frame or out of allignment. Again, this noise is directly related to the engine reaching and maintaining 'normal operating temps'. This is starting to make me feel stupid...what am I missing???

 

Finally gave in and took the Blazer to Chevy to have them diagnose the noise source...their prognosis was that I had replaced my Belt Tensioner (2 months ago) with a 'cheap' brand that had gone 'bad'. Chevy gave me a repair estimate of $350 or so to replace it with the 'proper' AC Delco brand...REALLY??? Anyway, got the AC Delco tensioner (actually made by Gates) and a new belt on line...no change (thanks Chevy...I am trusting my own troubleshooting after that episode). So, the belt drive system is NOT the source of the noise. Only one option left; disable the Balance Shaft.

Once I started removing the Harmonic Balancer (I have done this before), it was really not budging and I tried a different strategy on my puller placement...NOT A GOOD IDEA! The outer portion of the Harmonic Balancer popped off in my lap! I didn't know it was a 2piece part (with a rubber ring between the 2 portions). Okay, lesson learned! Once the balancer and timing cover were off, I loosened (not removed) the Camshaft gear bolts (for clearance), unbolted the Balance shaft drive gear bolt (a female Torx socket is needed for this), removed the gear and left the shaft in place and put it all back together. I was dreading the so-called 'low-rpm' roughness but was pleasantly surprised with a hardly any change in motor vibration. Only one day of driving, but the Rattle is gone!

 

I know this is an old post but I have a rattle coming from to me sounds like the lower end u can hear it under a load. It's not obnoxious but irritating. What exactly does the balance shaft do

 

The Vortec V6 is basically a V8 with the rear cylinders lopped off! The balancer shaft is a pre-weighted rotating shaft to imitate the missing cylinders...this keeps the engine smooth during low rpm's. I actually returned the above mentioned balance shaft I had removed back in place after having to go back in and install a timing belt tensioner kit.