Ominous clicking/tapping frm RF of engine

How many miles before the next oil change? I have heard of the lifters in some cars getting noisy right about the time an oil change is due. Oil filter brands have been beat to death in this NG, but all seem to agree that a good filter like the OEM or WIX for example coupled with possibly a different weight oil (I use a 10W30 synthetic) is the key in their cars to get rid if the HLA noise. MY 91A never had any of that, but I have changed the oil much sooner because I am lucky to drive 3-5k miles a year.

Just a thought.

clicking/rattling sound at lower rpms--at higher revs the noise is not noticeable, but at lower revs the clicking can be heard--it seems to be emanating fom the right front of the valve cover (maybe the nose of the right cam?). The car was professionally maintained until I bought it (14 mos/35 k miles ago)--since then I've changed the oil regularly (every 3,000 mi). i just noticed this for the first time a few minutes ago, and have not had the opportunity to delve further. Any likely causes? Any info would be appreciated.

If it's loud, it's HLA clatter. If not, it's normal injector noise.

Leon