Sharp grinding sound when letting off throttle

[swatvan]

Hi,

I recently replaced my alternator, alternator belt and ac belt, 2 days after the replacement I started hearing a grinding sound when letting off the throttle which lingers for a couple of seconds.

The sound is consistent throughout the rev range but only when letting off the throttle - The sound occurs when in park, neutral and drive.

Let me know what you guys think - I'm going to have a proper look this afternoon and put my old belts back on to see if there is a difference.

Car: 2.5i Auto Sedan (Gen 4 / BL)

[Yowie]

Idea 1

Tension on the accessory belt the drives the alternator is adjusted with that long threaded thing on the driver's side of the alternator. The belt could have been made too tight or too loose on installation of the new alt?

Perhaps experiment with belt tension to see if the sound is still there?


Idea 2

Do you still have the old alternator?

If so, for the sake of 10-15 mins putting the old one back in it could be worth the experiment to see if the sound is specific to the new alternator.

[swatvan]

Thanks for the reply Yowie,

I played around with the belt tension for the alternator belt & ac belt but didn't have any luck directly affecting the sound.

Unfortunately my car died yesterday which led me to believe the 2nd hand alternator I purchased and installed wasn't charging the battery and could've had a bad pulley.


So, I put the old alternator in, jump started the car, but the sound was still occuring.

On a side note: the car not starting was a result of a dead battery so I'm under the assumption both alternators I have are working/charging but aren't causing the sound


Me and my mates thought it could be the exhaust heat shield so I checked that, but it was already tight as, and after a bit more tightening the sound was still persistent.


I'm getting my car looked at tomorrow morning so I should have a good idea of what it will be sometime tomorrow arvo.

I didn't end up putting my old belts back on as they were cracked and didn't want to risk hurting the engine.


I'll post my progress tomorrow incase someone else runs into this issue again and finds this thread.

[RX25SE]

Alternator over-run clutch?

[swatvan]

So the mechanic has confirmed the sound is coming from my resonator.

Either the sound dampening inside of it gave way or a piece of kat is stuck inside of it.

If my kat has blown I'm thinking about getting uel headers: https://infernofab.com/subaru-2-5i-uel- ... steel.html

If my resonator has just gave way then I'll just get her chopped out if they can't get the metal out.

[Yowie]

I'm not familiar with the 2.5i. In that car is the cat and/or resonator part of the headers package? (as opposed to further downstream)

[Tonic]

If it is a bit of Kat stuck wouldn’t it be more of a meow sound?

[bigBADbenny]

Try a catalytic converter temperature test to confirm if the cats are working or not?
After a drive, on idle checks if the cars are hotter at their exits using a thermometer gun:
https://m.youtube.com/watch?v=9VZ5K8n5jj0