Odd rubbing noise

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Kidd-7

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RTP, NC
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96 Cougar 4.6L
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This is weird, very intermittent, best way to describe it: a rubbing / vibration noise almost like a fan bearing wearing out, not squealing though. This happened prior to replacing the rack, so not related. When it does happen it only lasts for 30 seconds or so, it may happen again in a minute or not for a few days later. The sound seems to come from the passenger side floor board area, may under the glove box.

Things I've tried when the noise occurs:
- Turn the heat off, thus blower and A/C; I really thought it was the blower, it's made noise before, but with the blower off the noise did not stop.
- Shifted into neutral
- Tapped brakes
- Revved engine

Other things I've noticed:
It is always the same tone, not speed dependent, not RPM dependent. Very much like a hum.
It's only happened on city streets, not highway, so speeds around 40 to 60 mph.
Going straight not turning & maintaining speed, not slowing down, not accelerating.
It has happened on different streets, so not some asphalt abnormality.

I think that covers all I've noticed. Any thoughts / ideas are much appreciated.
 
Kidd-7 said:
It's only happened on city streets, not highway, so speeds around 40 to 60 mph.
Click to expand...

Pretty fast-paced city you live in!

I have a hard time coming up with any suggestion because you pretty much covered all the usual suspects in your diagnostics.

Could it be related to interference in the speaker?
 
Well country roads and there is this main drag that's 55.

Speakers, good thought, I've not gone through the stereo yet, but I do know who ever put this one in did a hack job. It's been on my to do list for years now.
 
It's not the speakers. One recent time it occurred I thought I felt a load on the engine, so I pulled over and unplugged the low pressure AC switch so that the compressor wouldn't cycle. Well with that unplugged it still made the noise.
 
Did you rule out any odd blend door activity? Do you have manual or automatic A/C? I think the blend door still operates even if the fan is off (?).
 
had not thought of that. It is manual and I did turn the knob to off once when it happened and it was still making noise. That is vacuum driving though, may still be rubbing something.
 
Kidd-7 said:
That is vacuum driving though, may still be rubbing something.
Click to expand...

The blend door is electric. But on a manual system it only operates when you turn the dial I would think.

I was thinking that, on the automatic system, it could make occasional adjustments which could cause your symptoms.

So look elsewhere I guess...
 
OK car was warming up the other morning and the noise started, it’s much louder outside the vehicle than in the cabin. I gave it some gas and the noise changed, so now I’m thinking it’s a pulley.

I replaced the power steering pump and idler pulley when I did the rack so not those.

I’ll have to pull the belt and see if any other pulleys make noise or feel funny.

I’ve replaced the water pump and harmonic balancer before, that narrows it down.
 
Got a mechanic's stethoscope? Put that on the accessories. You'll find the noise real fast.

My vote is alternator based on what you described.
 
Recently found the LSC sounds like hamsters on a cold day. Hopefully just the belt. Maybe I can borrow a steth
 
IAC
Mine can make a hum/howl, and i can accelerate it away, or turn it off and restart and it goes away.
It happens more often when i haven't driven the car for a prolonged period.
 
Yes, they do. its a resonance in the inlet tube excited by the throttle position, and iac operation. It seems to be a sticky iac, bouncing around, and hitting a resonance, but I can't prove that. Popping the throttle makes it go away for a bit.
 
Yes I do have a mechanic's stethoscope and can give that a try.

I replaced the IAC; but that's probably been ~5 years ago. Does the IAC modulate? I thought it was either open or closed and wouldn't be frequently on / off.

What can I use as a lubricant that is safe for the intake? Or just clean any soot outta there?
 
Iac is a variable opening. The inlet tube is known to honk like a goose.
 
could you possibly have a bad motor mount that isn't totally broken but cause an odd shift in the engine? (just a thought)
 
Lol. Fix your engine mounts; You do not want to do the fun drive I did, at wot. The problem with the 4.6 is that the drivers' mount goes bad, the engine twists up, and stuffs the throttle body blade lever into the hood. Holding it wide open.
 
Sounds like fun grog..

Motor mounts are only a few years old also, but still worth a check.
 
Yeah the noise resonates all over the place. I’ve had some good luck and some bad finding noisy pulleys.
The problem in diagnosing this is it’s very intermittent.
 
Not since the 70's lol. I was wtching seinfeld earlier, george drove peeple crazy.
 
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