Another knocking noise
 

Hi all, first post and what a way to start with engine problems already!

So about a week ago, my 01 WRX developed a knocking-type noise from the right side. It's barely noticeable from the passenger seat and from outside, but sounds like hell from the drivers seat!
It's done 108k, oil/filter changed 1.5k ago with Millers CFS 10w-40, and did the cambelt and pulleys this Wednesday, tensioner had been making contact with the block and the small pulley was wobbling/squeaking. But this didn't fix the knocking.

It's noticeable for a split second on startup, then not heard again till the engine is at idle rpm ~750. The volume of the knock increases if sitting idle for a few minutes, and when turning the wheel on the spot. Frequency also follows RPM, audible under load up until ~4500rpm, noise dissapears when decelerating off throttle until at idle speed again. Sometimes feel the knocking through the steering wheel, brake and clutch pedals. Hasn't got noticeably worse over the few days I have 'had' to drive it, and hasn't affected driveability, pulls fine throughout each gear.

So outside the car and under the bonnet it isn't very audible at all, but underneath you can hear it more. I've been under with a long screwdriver to listen with, and can't seem to narrow it down, exhaust shields and up pipe are solid, and can't find an external source for the rattle with a rubber mallet.

Also no fault codes have been logged, no warning lights, oil level is fine. Should also mention it makes this noise hot or cold, just more noticeable at low rpm.

Sorry for the mega wall of text, but it's bugging me that I can't find the source of the knock! Any ideas?

Cat broken loose in the downpipe ??


Mick

It's a full decat system, as far as I'm told by the previous owner anyway, I'll check for a sports cat next time I'm under the car, thanks

What fuel are you using? I've had pinking before on my old m3 when I ran 95ron. When filled up with 99ron all was good. Just a thought

Just recently only sainsburys premium, which is 97 ron, but only because I haven't been near a shell garage. Normally use V-power, I'll fill up with that next and see what happens, though it doesn't sound like pinking from bad fuel, detonation etc, worth a try though if it helps. Thanks