Metallic noise

[jlfernan]

Seven year old MK IV. Blueprint 302 with Quickfuel carb. Between 2500 and 3000 rpm I get a metallic sound that sounds like a metallic plate vibrating. Not the pipes or heat shield (pipes are new Gas n Pipes). Driven without the heat shelf shield. Have been all over the car and can’t find anything loose. It lessens after driving a while. Any ideas?

[rthomas98]

Do you hear the noise when the car is under load at those RPMs or when it is parked in the driveway with the hood open or both? Pinpoints whether directly engine related or if it is resonance somewhere else then the engine.

[PNWTim]

Also, do you feel it as well as hear it? That can eliminate a lot. Lessens after driving awhile would typically indicate something expanding with heat.

[jlfernan]

Do you hear the noise when the car is under load at those RPMs or when it is parked in the driveway with the hood open or both? Pinpoints whether directly engine related or if it is resonance somewhere else then the engine.

Always under load. I'm leaning toward resonance, just can't figure out where. I was hoping someone else hade encountered this before and could point me in the right direction.

[boat737]

Early on I had an annoying rattle/squeak. Like you, it seemed to only occur under certain conditions. Took a while to figure it out, but finally found that the one leg of the roll bar was just touching the hole in the body and the trim ring. I put just a dab of silicone lube, and it's been quiet since. Also, since it was the body making noise, it sounded like it was coming from different places, and not so much where it was actually coming from.

So (assuming it's not engine internals), I would suggest checking panels, brackets and body for any interference, flex, or loose parts. A small rubber mallet with some gentle tapping on the heavier parts may help you find it. It's a daunting task, but you'll find it.

[cob427sc]

You can also check the metal plate between the engine and transmission (if you have one). I had one the drove me crazy every time I pushed in the clutch to shift.

[CraigS]

This may be hard to find but you might consider that a noise under load at 2500-3000 is a classic symptom of engine knocking. I fought that at one point and discovered that the vacuum advance allowed 20 deg advance on top of the mechanical advance and it was slow to retard as I added throttle. I fixed it by limiting the vac advance to about 8deg. You could experiment by adjusting your base timing maybe 10deg less than it is now. Yeah your idle will be low, and the engine will probably feel weaker, but it is just an experiment. Also verify how much timing you have and how it changes. You could have too much base timing or too much mechanical advance.

[Blitzboy54]

Roll bars maybe? Check to see if the bolts are still tight?