"william kossack" wrote in message
news:K2OTb.213579$xy6.1102525@attbi_s02...
I have a grizzly g8691 lathe.
It seems to work OK but at higher speeds it produces a knocking noise.
I'm going to try and take the cover off this weekend if I get the time
but I'm wondering what the noise could be?

Maybe you should switch to a higher octane fuel.