First and formost, knocking is BAD!!!!! It is not a good idea to drive around while it is knocking.
Second, get a timing light.
Third, everyone has an opinion about timing, engines and the universe. If it is knocking at 39 total advanced, you may want to try premium gas, octane booster and a little lead additive. Then again, you could, using a timing light, back off the timing even more. Too little will cause backfiring and really sh!tty drivablility.
fourth, if you drive around with a constant knock, you could pop a hole in a piston.
Hope this helps.
