Annoying engine rattle

[IVIUSTANG]

Hello again!

I have had an annoying engine rattle for the last 200k I have owned my car. I do all my own maintenance so I know everything is tight. I have checked and tightened brake lines in their clips, liners, metal heat shield etc.

It sounds like a bad bearing in a pulley or something and only happens at certain RPMs, resonates pretty annoying at 1500RPM. If I rev the car in neutral the rattle comes back as the RPM is falling at between 1000-1500RPM. Seems to get better as the car warms up a teensy bit. Today I replaced the serpentine idler and tensioner with zero change in the noise(it had 340k KM on it). I also checked the AC compressor and power steering/alternator pulleys when I was doing that and they seemed smooth and tight.

Is it a bad idea to take off the serpentine belt and idle for a minute or two and eliminate anything there as a possibility?

Thanks,
Jesse

[Astro14]

Sounds like exhaust to me...but still, it won't hurt anything to idle the engine with the accessory belt removed, because the water pump is driven by the timing belt, so you'll still get cooling...

[Antherzoll]

Check the downpipe support bracket, I've had rattles come from the brake lines not being supported correctly (they should be seated tightly in clips on the braket) and the DP support arm contacting the frame.

[billr99]

Check the alternator pulley. If it's never been replaced you are well past due (INA recommends replacement at the same time as the serpentine belt). Its the clutch in the pulley that goes and if it locks solid, or close to, it will display the sympthoms you describe. At least it did on my '02 at about 337K kms.

Best way to check is to pull the serpentine belt off and see if the engine smooths out.

Cheers,

Bill

[IVIUSTANG]

Thanks for the direction, I'll check all of these in the next couple days and reply back.

Jesse

[IVIUSTANG]

Took off the serpentine belt and checked the alternator pulley again, it is tight, smooth and only turns in one direction as it is supposed to. I then left the serpentine belt off and started the car, the rattle was still present; now I know the noise is not related to anything rotating(I have done timing belt on this car with water pump/tensioner and pulleys with no change in noise then either).

I looked around at the back of the engine and banged stuff around and the exhaust and heat shields etc seem very solid.

I did find the power steering hose where the rubber meets the metal line is resting loosely on the subframe; I'll have to play around with this a bit more when I have another person to rev the engine to the correct RPM to make the rattle; I'll dig deeper on Saturday and slay this annoying beast.

Thanks,
Jesse

[Xfingers]

Maybe check the exhaust system as Astro14 suggests. PO did the JRL resonator mod on my exhaust. That new piece of exhaust pipe has since rusted and partially broke loose from where it was welded in place. I wrapped a band clamp around the junction as a temporary fix. Now when I start the car cold I get a rattling for about 3 min. then everything quiets down. I'm guessing as the metal gets hot and expands, things tighten up around that exhaust joint and the rattling goes away.