Pug1off or Lynx bottom pulley

[Rippthrough]

It's not as immediate an effect with cars, as they tend to only spend brief periods in the problem frequencies, as the rpms are always changing. Much more readily show with working engines which tend to be running within a few hundred rpm all the time.

Still, the damage it can eventually cause is undeniable. But then most car engines that are being tweaked probably won't be expected to do another 50k miles anyway.