Have Valve train noise at 56,000 miles, engine oil and filter changed, drove about 70 miles have ticking noise that comes on at higher engine speeds, such as just before the auto trans 1-2 shift or above 45 MPH at constant throttle, letting off the accelerator ticking goes away, comes back as accelerated. car sat for about 6 yrs before this. Hard to get ticking noise just free reving engine with hood up have to rev engine to high rpm. Engine is quiet at idle and smooth. The ticking noise doesn't always come in at the the same speed and is louder some times. Have valve cover off, can't see any broken or loose. pieces, checked with magnet, nothing. Tried pushing down lifter end of rocker arms with engine at idle, all made about the same noise, only one a little more took rocker and lifter out nothing visable. If I remove all rockers can I measure the overall height of valve/retainer/spring to determine if the valve seats have moved or sunk? THKS