Rattle/Clank noise in engine bay, only in "Drive" and under acceleration (video included)

SOLVED 7/15/23: I had the drive/serpentine belt routed UNDER the idler No. 2 pulley, not OVER. I corrected the belt route, and the sound is gone.


I recently did a list of maintenance work on my Tacoma, and a few days after (not immediately) I started getting a metal-on-metal rattle/clank noise in engine bay on the front drivers-side.

It happens while stationary or moving and hot or cold, but it must be in gear and under acceleration between 700-900 rpm.

I've checked all throughout the bay and can't find anything loose, and re-set the skid plate, but I can't track it down.



Model
- 2013 A/T 4.0 Prerunner w/100k miles

Maintenance completed (prior to noise)
- Spark Plugs (replaced w/ OEM)
- Drive/Serpentine Belt (replaced w/ OEM, but belt was slightly offset on 1st start and I immediately corrected it)
- Air filter (replaced w/ OEM)
- PCV Valve (replaced w/ OEM)
- MAF (cleaned)
- Throttle Body (cleaned)
- Rear Dif (fluid changed)
- Power Steering (fluid changed)
- Brake (fluid changed)

 

Video is showing up as this microscopic player on my PC. Any way to share a larger video or upload on the ol' YouTube?

Maybe I'm just trying to see things that aren't there, but in the super teeny tiny video it looks like your belt is flying around all crazy like. Since you just changed it, and if the larger video looks the same, you might want to start there. Double/triple check it is routed correctly. If it isn't, or if something else is wrong like a bad tensioner/pulley it could be making weird metal noises like a pulley bearing got roached.

Spark plugs or MAF are the other fringe items to check. MAF if you cleaned it wrong could mess up the A/F and make it run bad but I don't think the video shows that. Spark plugs if you got some counterfeits could be running on not all 6 cylinders but again video doesn't really show that. Everything else on your list would be pretty hard to screw up and make noise in the engine bay so my money is on the serpentine system.

 

Here's the direct link to the video, hopefully it will be better https://vimeo.com/manage/videos/845038284.

The thing you see flapping is just a loose piece of electrical tape. I've since broke that off. The spark plugs are OEM (Denso), but I picked up a mechanic's stethoscope and it seems to be coming from the AC compressor (or just maybe the alternator). There's no change whether the AC in enabled or not, and it only knocks between 700-900 RPM.

Do you think I could have damaged the bearings?

 

Well I'm shamed to admit, but the issue was as simple as a misrouted belt like wi_taco suggested I check...

I had the belt routed UNDER the idler No. 2 pulley, not OVER. I corrected the belt route, and the sound is gone.

I'm sorry for wasting the time of those who read through this.

 

You need a serp belt sticker. Click the link in my sig.