Intermittent rattle
 

There is a intermittent rattle that is coming from my BRZ. At first I thought it was the alternator pulley, so I replaced the that, along with 1 tensioner pulley, 3 idler pulleys. Attachment 213191 , everything that’s circled blue and red I’ve replaced. There’s also i video i attached, the thing is I can hear it more clear underneath the car.

Mine sounds similar, does it come and go with turning the a/c on and off?

Probably the alternator itself, that grinding is muted enough that I'd assume it's internal to something (not a pulley bearing) but who knows

Interesting one. More rattle than grind. Have you listened from underneath? Auto, or manual?

Maybe the water pump is going bad.

:iono:

I suggest you use the old long screwdriver to the ear to see if you can isolate where the sound is coming from.

I thought about that but, man, if that sound was the water pump, I imagine it would be pissing coolant.

One of my family members made the original post about the issue I'm having.

Few Clarifications:
-Replaced the alternator with another used alternator from Ebay
-Replaced Belt
-Replaced 2 Smooth Idler Pulleys
-Replaced 1 Grooved Idler Pulley
-Replaced Tensioner
-Manual Transmission for the 2017 Series Yellow BRZ

I find that the rattle comes one after the car warms up after a cold start. Also, it's more obvious when the AC compressor clutch engages, but I found any large electrical load brings the rattle back (Ex: I turned off AC but then turned on seat heaters and defrosters and rattle came back).

I usually can only hear the rattle that comes and goes while idle sitting at a light.

I was going to try to track down where the noise is the loudest using a Mechanic's Stethoscope and possibly going underneath and removing the shield and seeing if I can find anything rattling around...

Does it go away when pushing the clutch?

pull the belt and run it for a few seconds like that. Then you will know if its from something belt driven, or something in the clutch, timing chain, valve train or other stuff

Sounds like the alternator. You turn on AC, noise. AC off, no noise. Seat heaters and defrost, noise. Only way a seat heater and defrost would cause issues is a change of load in the alternator. AC would use more juice as well running the magnetic latch for the compressor, and your fan.

Especially since you've changed so much already. Could be bearing in the alternator starting to go and making noise when it's experiencing higher loads. Subi alternators are known to be one of their more frequently replaced parts over the life of the car.

My 01 Outback broke alternator bolts three times, but never made any noises.

So to give an update:

I was hoping it would get worse but somehow after a few weeks of my post the noise went away and has remained mysteriously gone. Maybe those components I replaced made a difference eventually? I don't know seems weird maybe it'll come back in a few months.

This experience did make me an expert at getting the accessory belt/pulleys on and off so guess I got something out of it.