Rocks or thunderWhen you purchase a brand new car, everything is finely tuned, literally. The acoustics of the car’s drivetrain are thoroughly tested in a variety of real world conditions with all the different drivetrain combinations available to ensure the engine, cams, exhaust, etc. aren’t vibrating at the perfect frequency to make a horrible racket.

In the aftermarket, there are seemingly endless combinations of engines, transmissions, cams, and other drivetrain components available to choose from and sometimes that beautiful bass you expect to hear coming from your car sounds more like a box of rocks or a jackhammer. However, we have few tricks of the trade to make your car run quieter whether it’s the driveline harmonics or something else.

If your harmonics are off causing a “box of rocks” or “jack hammering” sound at low idle rpm, bumping up the engine idle 200-300 rpm will usually solve the problem. If that doesn’t work, change over to or replace deteriorated rubber mounts, change to a sprung-hub organic-face clutch, check to see if the body of the car is touching the transmission or bellhousing, add sound dampening materials, or if possible/advisable, change from a steel to aluminum bellhousing because steel bellhousings can sometimes amplify noises just like a bell.

If you hear a sound coming from the transmission in neutral that goes away when you press down the clutch, this is a sound referred to by TREMEC as “neutral rollover”. It’s the sound of the transmission rotating without load. This can be deadened by a variety of materials designed to deflect heat and sound coming through the transmission hump of the car. You can choose from mats or painted-on materials. Some are designed to fit under the car and some under the carpet.

If you’re hearing a “groan” coming from your transmission under load when you are or are close to lugging your engine, it may sound concerning, but your transmission is OK. And the fix is simple; stop lugging your engine! Plus, you can damage your engine when you lug it; check out this explanation from “Engineering Explained”.


However, if you’re building a high-performance car to make more power, the exhaust louder, etc. you may to come to a crossroad where you will have to decide if you want all out power or a quiet cabin because in some cases, you can’t have both.