Tracking down a noise...

So over the last few weeks I've noticed what I would describe as a "chirping" sound which I think is coming from the engine compartment. It only occurs when I am accelerating from a complete stop. It goes away after a few seconds. It does not occur every time I accelerate from a stop. It does not occur when I rev the engine with the truck in park. I replaced the timing belt with the Aircabinman kit about 6 months ago, so I hope that eliminates all the idlers and tensioners. I used a mechanics stethoscope and, probably because I only notice the sound under acceleration, I can't track it down. At this point I'm wondering if it could be a belt though they all seem tight and I would think they would slip whether the truck was in motion or at stop. My next thought is the fan bracket or the fan clutch. Does the fact that the sound only occurs when actually driving point to anything? Since It only occurs when moving, I guess it could be a wheel bearing or the drive shaft. Hoping for something easier/cheaper...

 

I'd rule out the AC idler pulley. Gently place the tip of your stethoscope on the bolt that runs through the pulley. It does sound belt related. But then again it sounds similar to a throw out bearing noise that a manual transmission can make. Not sure if auto trans can make chirping noises. Might try using the stethoscope while someone else revs the engine in park. You may struggle hearing it in park due to fan noise. Consider turning on the AC while idling then checking around the compressor with the stethoscope (or does this noise happen with AC off too when driving?).

 

I had a chirping noise that would only manifest itself at low speed on rough roads. Had me concerned it was poly UCA and LCA bushings I changed earlier this year. A couple weeks ago I shot some white lithium grease on the hood latch assembly and the hood hinges. Heavenly silence. The point is, it may not be related to the engine at all.

 

Doesn't seem to matter if the AC is on or not, but I will check that. It's pretty loud when driving so I think I would hear it over fan noise in park.

 

I'll give that a try.

 

Can confirm that the sound occurs with the AC off. Definitely sounds rotational in nature. I'm mostly stumped as to why it only occurs with the truck moving. Would wheel bearings "chirp" for a few seconds and then stop or grind? Front brake pads and rotors are fairly new as well. Replaced those about 20k miles ago.

 

Jack up the front and rotate the wheels and see if it's your bearings are going bad.

 

So I found the source of the noise...



And fixed it.

 

Good catch!