Sounds like you may have an oil pump close to failing? Kinda hard without actually hearing it myself.
I would triple check the clearences again to be sure. As well as the cam timing marks. They need the little dots and dashes to be inline with the oposite side saying "TOP" at the top. Left cylinder should be at Top Dead Center then. Sometimes you have to rotate the motor several times to get it right as the cylinder goes two full turns before it is at the correct timing position.
Also, check that you have the intake/exhaust cams in the right positions.
Not saying they are off, just double and triple check everything!
