2015 Silverado 1500 Screech Sound

[2004crewcab]

Hey all.........Thank you in advance.  Need some help pinpointing what this sound could be.  2015 Chevy Silverado 1500 5.3......194k miles.  Yes.....I know I'm on barrowed time with the 6L80 transmission, but it's shifting smooth and runs great.  I bought the truck with 170k, but it was VERY well taken care of with all the service records available.  I knew going into this that I'll be replacing the transmission at some point.  When I purchased the truck I added the Shift Technologies Sure Cool Kit and a Range AFM disabler.  

 

I've noticed somewhat of a lack of power when trying to pass in the last couple weeks, and slight chirp/squeak sound when demanding power.  I was towing my boat the other day and noticed the sound getting much louder and more frequent.  Transmission temps never got above 174deg.  The sound seems to be coming from the bellhousing area but more towards the starter side.  Put the truck on a hoist to investigate further.  Below is what I've already checked.

• Dropped the transmission pan to inspect and change fluid/filter.
  • Fluid was clean and zero signs of contamination
  • Split the filter and found very little contamination in filter element
• Pulled the starter to inspect starter hang-up
  • No signs of contact on starter gear or flex plate
  • Inspected flex plate for cracks
    • No signs of cracks visible and all seemed tight

When starting the truck there's a slight screech then goes away within 1 second.  The truck is quiet when idling and low RPMs.  As soon as you increase 2000+ RPMs the screech sound can be heard.  Higher the RPMs the louder the screech.  It's present in forward and reverse over 2000 RPMs.  Cruising down the highway below 2000 RPM the sound is very low and can't be heard.  As soon as you demand power the screech is there.

I've been discussing this sound with every mechanic I know and there's no definitive answer.  Below is a list of possible sources of the sound per the many mechanics I talked to.

• Torque converter coming apart
  • Shouldn't there be contamination present?
• Transmission pump failing
  • Shouldn't the sound be there at all times and see contamination present?
• Warn clutch bands
  • The sounds seems to be right at the bellhousing
• Catalytic converter coming apart
  • This is in line the lack of power and the screech/whistle sound with higher RPMs

 

Looking for some insight before I start tossing parts at the truck, especially dealing with expensive parts. 

 

Edited May 28, 2025 by 2004crewcab
Added picture

[2004crewcab]

Wanted to report my findings for someone that may have the same symptoms.

 

Bank 2 catalytic converter was completely gone and plugged up the downstream cat.  Replaced the cat assembly and I was still getting a squeal, but not nearly as loud.  After further investigation I found the #8 cylinder exhaust manifold bolts were finger tight, probably due to the back pressure with the plugged exhaust.  Snugged up the bolts and back in business.

[UrbanRage]

Glad you got it figured out.