So after a good solid afternoon of searching NASIOC for WRXs of my model year with similar conditions, I came to the conclusion that my sound was at least different enough to justify a separate thread. If this is an easy answer and I simply overlooked something, well... I tried.
I got into my car one morning two months ago, started it up, and finished my phone call as I began to buckle up. When all of a sudden...
Conditions of the symptom:
- 2002 WRX - 170K miles - Original engine, no rebuild
- Ambient Temperature: Both Cold and Hot (-10 F to 80 F)
- Duration: A little more prominent at start-up but still present after complete warm-up (Intensity is reduced perhaps 10-20% after warm up)
- Sound matches RPM's almost exactly (1 sound per RPM or 1 sound per 2 RPM)
- Most audible at idle in gear and neutral with clutch both in and out, but slightly more audible under load when accelerating from 750-1800 RPM's then falls off quickly after that
- Tone is incident to a small knocking sound almost like a clicking
- Sound appears to be coming from driver's side (90% certain)
- Sound appears to be coming from front of engine (50% certain)
- Sound is barely audible and you wouldn't notice it unless you were listening for it like I was. Once you hear it though, it is distinct enough to catch every time it happens.
Given the symptoms I've compiled a list of possibles, some of which are much more likely than others:
Bearing failure (perhaps one of the journals?)
Bad Alternator (Bearing or pulley)
Bad AC Belt Tensioner
Unfortunately I can't just tear apart my engine on a whim, nor can I afford to have a shop tear it apart without being absolutely certain of what I'm getting into (to put it bluntly, I'm broke, in between a rock and a hard place, with no way out). Suggestions would be most appreciated or even things I didn't consider. I'm working on getting a logging cable so I can check AFR's soon to make sure engine knock isn't a possibility.