Engine Ticking under load....Valvetrain???

I have a 2002 Rover Disco 2 4.0L with 70k miles. After engine warms up it starts to tick over 1/2 throttle or approx half load. It always does it after a freeway run, but after about 5-10 minutes idle or easy city driving it fades, and even goes away. When its cold I can open it up to full throttle and it wont do it(no ticking). 1 or so, out of 20 cold starts, it will knock/tick once or twice and instantly quit. The ticking noise is light sounding, like valve train. Not rod knock sounding. I tried the float test. Sticky Valve? Bad Lifter? Bent Push rod? I saw this question asked on another forum a while back, with exact same symptoms, but it had no answer. Hopefully this is a common Land Rover issue and someone knows something.