I own a 02" Corolla with 2ZZ-GE engine. About a year (12 000km) ago I have rebuild engine myself. Manual gearbox was rebuilt too, but by service guy. After rebuild everything was working fine, except for unusually noisy gearbox.
Recently, about a week ago engine started to knock silently, and knock is more loud every day. Knock is audible only on acceleration from low rpm's (like 600), and almost disappears at about 1500 rpm. More engine load generates louder knock. The knock sounds like diesel engine, or tapping two wooden sticks. There is no knock at higher rpm's and engine easily accelerates to redline. ECU diagnostics doesn't show anything unusual.
What are possible causes for that knock? Thrust washers? Gearbox? Anything else?