Just to get everything possible on the table:
Intake leak causing motor to go lean under acceleration might be a possibility.
Might check for higher than expected
oil consumption (not sure your motor is susceptible to this so others might have good info). If the motor can suck
oil, it will cause hot spots as well and really make a noise under almost any kind of acceleration. You should see a bit of smoke on early acceleration on the side leaking (again, if that motor is susceptible to internal intake leaks).
Does sound like the knock sensor though doesn't it.
Good luck.