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Discussion Starter #1 (Edited)
I'm getting an intermittent low pitch grinding/rubbing noise which sounds like its coming from behind the right side of the drivers seat. Now, I'm in a RIGHT hand drive country so for the south paw countries, this will be like its coming from behind your passenger seat.

From the outside, I tend to hear it from the right rear tire well closer to the vent cooling than the rear bumper.

Observations :

1. Loudest ( and I exaggerate "loud") and most frequent when the car is cold and at start up.

2. In drive gear (PDK) and when I lift off the pedal from standstill without depressing the accelerator, it grinds/rubs for like a second. No issues when accelerating.

3. The reason I think its may be an aircon related issue is there does not seem to be the grind/rub when the aircon is not switched on. Thing is I'm wondering what aspect of the aircon (compressor?). Is the water pump linked to the aircon and if so could it be the water pump?

4. My serpentine belt is fairly new and changed less than 2 years ago and with less than 15k miles after change.

5. Car is just past 10 years old and aircon has not been changed since I took over ownership more than 4 years ago.

6. No fault codes.

Any ideas where I should start to look? Again, its intermittent based on the above, not loud at all but its there, and its a daily thing so it gets irritating.

Thanks.
 

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AC compressor is on the left side, toward the top of the engine. These compressors are always "on", meaning there's no clutch. Internal valves control the pressure. There only noise you're likely to hear is if the pulley bearing is worn. The pulley (or just the bearing) is easily replaceable with the proper tools.
Yes, it is driven by the serpentine belt. I don't think your noise is the AC compressor. More likely the water pump or some other driven accessory. Possibly the idler pulley.
 

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Discussion Starter #3 (Edited)
AC compressor is on the left side, toward the top of the engine. These compressors are always "on", meaning there's no clutch. Internal valves control the pressure. There only noise you're likely to hear is if the pulley bearing is worn. The pulley (or just the bearing) is easily replaceable with the proper tools.
Yes, it is driven by the serpentine belt. I don't think your noise is the AC compressor. More likely the water pump or some other driven accessory. Possibly the idler pulley.
Thanks. If the AC compressor is on the left side, its definitely not it.

I'm reading that the water pump is part of the system to keep temperatures in check at all times. Does the water pump work HARDER when AC is switched on and maybe that causes the grind sound only when the AC is switched on? I tested for the grind sound again today with AC on and AC off. The sound is there (intermittently per my description above) only when the AC is on.
 

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Thanks. If the AC compressor is on the left side, its definitely not it.

I'm reading that the water pump is part of the system to keep temperatures in check at all times. Does the water pump work HARDER when AC is switched on and maybe that causes the grind sound only when the AC is switched on? I tested for the grind sound again today with AC on and AC off. The sound is there (intermittently per my description above) only when the AC is on.
There is no direct connection or correlation between the water pump (engine cooling and cockpit heating) and AC (cockpit cooling) systems. Even in the heater core and chiller coils under the dash - they are separate systems. Of course, running AC puts a greater load on the engine and that increases slightly the amount of heat the water pump and radiators need to dissipate.

Rather than conjecture, I recommend removing the firewall engine cover (behind the seats) and try to isolate where that noise is coming from. It is a little work to remove the carpet and trim but once opened, the whole front of the engine is exposed. A mechanic's stethoscope (or even a small hose held to the ear) can by used to pinpoint the sound.
 

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Discussion Starter #5
Thanks again for chiming in. I think I'll have my mech look into it at the next service. I'm really not good mechanically and don't have the tools or skills to go this deep.
 

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I think I'll have my mech look into it at the next service. I'm really not good mechanically and don't have the tools or skills to go this deep.
That's probably the best idea. If you notice it getting worse, take it in ASAP.
 

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for strange noises, the first place to check is as RSchewerer mentioned - open the panel behind the seats. there are a few components that are common noise points - not just the belt and pulley but also the water pump, belt tensioner (which cause different rough bearing type noise), power steering (this is usually more a groaning sound though).

in my case, the water pump and belt tensioner + the belt were the culprits.
100,000 Kms (60k miles) Water Pump, Belts and tensioner...
 

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Discussion Starter #8
for strange noises, the first place to check is as RSchewerer mentioned - open the panel behind the seats. there are a few components that are common noise points - not just the belt and pulley but also the water pump, belt tensioner (which cause different rough bearing type noise), power steering (this is usually more a groaning sound though).

in my case, the water pump and belt tensioner + the belt were the culprits.
100,000 Kms (60k miles) Water Pump, Belts and tensioner...
Thanks.

I don't think its the power steering or rather hope its not as Porsche changed my power steering under warranty about 2 years back. This should be some where close to the steering column (?) and if so, its not the case as my sound is coming from behind our side side drivers' seat.

I suspect the water pump but then again, maybe not as I don;t have any over heating issues. Hopefully its just the serpentine belt that needs some tension?
 

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Discussion Starter #9
Had my mech take a listen to the sound today. He says its the lever tensioner and tensioner damper like what Eye shared. May as well get that fixed at the next service.
 

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Discussion Starter #10
I checked my invoice when my major service was done in Dec 2018. So it seems the Tensioner lever, hydraulic and roller plus the serpentine belt were changed by another Indie shop that I've stopped going to.

So question 1. How often do these parts need to be changed? 1.5 years seems often.

Queston 2. If its not the tensioner, then what else make cause this sound?
 
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