aroundtuit

Have a 2016 Z06. Noticed last fall an intermittent faint noise when going at a steady highway speed. Slight change of speed and it goes away. Brake or turn and it goes away. Took it to my Chevy dealer who has a dedicated Corvette mechanic that I trust. He couldn't get it to make the sound but did notice a leaking tensioner and replaced it. That didn't solve it. Recently noticed that it happens right before AFM switches from v4 to v8. Sound comes from the driver side under the hood somewhere. Hard to describe the sound, kind of a gravelly sound for a few seconds, then ends suddenly as all 8 cylinders come back online.

Anyone had or heard of this issue? Trying to gather as much info as I can before I go back.

C7&7

I had a Silverado that made a hissing noise when it switched modes. I remember taking it in and the tech told me the sounds was normal and it was a valve or something.

stingraynick75

I had the same issue, replaced this and fixed it.

Vetteman Jack

stingraynick75 - thanks for posting that service bulletin.

aroundtuit

Thanks for the input. Mine doesn't sound at all like hissing.

aroundtuit

stingraynick75 Thanks for the info. Even though mine's a Z06 and newer, it sounds very similar. I'm thinking it's something with the AFM now. I've already replaced the belt tensioner since it was leaking.

jwmgr8

The AFM system is very complex electronically and mechanically. Not only are there many special engine mechanical "things" but near the rear just before the axle the exhaust has two valves that open and close based on 4cyl vs 8cyl.
If you don't like the weird sound you should get a range device and see if that stops the sounds issue?

Buddhaman

I started noticing a similar sound a few weeks ago. I thought it was a piece of plastic rattling until I started to notice when it occurred. Same as you, V4 mode when giving slight throttle but not enough to get into V8 mode. If I let off the throttle or I push enough to go into V8 it goes away. Easy to replicate but I'm not sure whether it's worth it to go to a dealer over it.

Red08

I had a 2016 Silverado. When switching from V8 to V4, it was quiet and seemless. On my 2014 C7, I installed a Range unit that works as advertised.

Rick14C7

I have that same issue, noise when switching between 4 and 8 cyl, and it always feels like some engine part fell off from my car! It's embarrassing, especially when my girlfriend hears it....

Tommy79

Try running in manual mode and see if the sound stops....

Buddhaman

I picked up a Range device for my car. V4 mode is always spotty on my commute anyway and I got tired of the noise when it thought about switching.

Vette Jockey

Good luck on fixing it! I do not hate much, but, pesky noises are the exception!.

aroundtuit

I will be taking mine to my dealer in the near future. Right now I'm dealing with a cracked rim. Got a low pressure warning returning from a weekend trip Sunday. Replacement on the way, much thanks to House of Wheels!

But on a good note, took a trip this weekend. Drove 600 miles in Manual mode and never heard the noise. Pretty much nails it down to AFM.

BTW, 25 MPG out, 21 MPG back (Head wind)
driving 75 MPH.


Crack on inner rim of rear wheel.

Rick14C7

aroundtuit - A wheel with cracked rim could disintegrate at high speeds. It's great you found it!

aroundtuit

Happened while driving on the interstate at 75 mph. Not exactly sure when/where it happened. The tire pressure warning came on at 24 lbs. I put air in it right away, slowed down, stepped up my pothole scanner, and kept an eye on the tire pressure. Judging by how much it leaked over the next 30 minutes, I estimated it happened an hour or two before the warning light came on.