Piston Slap: Caught in the Crossfire of drivetrain whine?

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Tom writes:

I have a 2005 base model Chrysler Crossfire with the six-cylinder engine. Recently I’m hearing a high pitch whine coming from the engine compartment after taking my foot off the gas. The whine will go away, only to return. I do a fair amount of highway driving, so typical examples are:

  • Cruising at 75 mph, foot off the accelerator, whine starts; foot back on accelerator, whine stops.
  • Cruising at 75 mph, foot off the accelerator, whine stops at about 50 mph or so.
  • No whine when driving around town.

I first noticed the whine a few weeks ago—just after having four new tires installed. I can’t imagine that changing the tires would have anything to do with the whine, but I thought I should mention it. Any ideas?

Sajeev answers:

Noises based on vehicle speed are almost never related to the engine, or anything connected to it via pulleys. Except for the fact that you hear it from the engine compartment, which debunks this conventional wisdom. That said, the first thing you should do is have someone remove the serpentine belt and test all the pulleys for squeaks, play, or grinding sounds.

Once the spinning things (technical term) bolted to the engine are given a clean bill of health, there are other load + speed-based whines possible from the front half of a rear-wheel-drive vehicle. A professional needs to check the transmission for issues with the torque convertor or any bearing failure inside (like the transmission oil pump). There’s a remote chance that collapsed engine mounts can also be juuuust bad enough to compound the problem at certain speeds and subsequently muck up the diagnosis.

And if that wasn’t a bridge too far away, maybe there’s some whispering gallery effect going on in your Germanic-American sportster and the differential is indeed the source of the noise. Because load + speed based noises are usually centered in the differential, so perhaps an inspection isn’t a terrible idea.

Let’s just hope you need a new pulley or something at the front of the engine. Best of luck!

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